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0331E5

Machine Gunner

E-5 (Sergeant) · Marines

E1–E3E-4E-5E-6E-7E8–E9
HEADS UP

Sergeant 0331 is the machine gun section leader rank — typically the senior NCO running the company weapons platoon's machine gun section (multiple M240 teams), or the senior NCO in a battalion-level heavy weapons section (M2 .50 cal / MK19 vehicle-mounted crews). The SSgt selection board (centralized, paper-record under MCO P1400.32D) is the next gate. Sergeants Course PME done; Career Course is the next horizon.

The Honest MOS Read
Sergeant in the 0331 community is the machine gun section leader rank — and in the Marine infantry's weapons platoon structure, the section leader job is the load-bearing combat leadership tier of the company's organic indirect/direct heavy-weapons effects. Doctrinally as a 0331 Sgt, you're the section leader of the company's machine gun section (typically multiple M240 teams plus the senior M240 gunners or vehicle-mounted heavy machine gun crews depending on the battalion's TO&E and current Marine Corps Force Design organizational structure — verify the current TO&E against the current MCO and MARADMIN updates), or the senior NCO in a battalion-level heavy weapons section running M2 / MK19 vehicle-mounted crews. The promotion math under MCO P1400.32D: Sgt → SSgt (E-6) runs through the Marine Corps's centralized selection board for the SNCO ranks — paper-record review of the full career package (FITREPs, awards, education, PME completion, MCMAP belt, composite history, conduct/proficiency marks, deployment record). Unlike the cutting-score system for Cpl and Sgt, the SSgt board is selection-based; the read is the read. The Career Course (Career School) is the structured PME at the SSgt tier and is required for promotion in most cases (verify current PME requirements against MCO and MARADMIN), but the Sgt-to-SSgt window is when you complete it and when the centralized board reads it. The section leader job content: you own multiple gun teams (typically 2-4 M240 teams in a company weapons platoon machine gun section, or multiple heavy machine gun vehicle crews in a battalion-level heavy weapons section), running the section's training (live-fire ranges, gunnery, MEU-SOC certification machine gun integration), the section's FITREP-equivalent (the Marine Corps's enlisted evaluation system) cycle for your Cpls and LCpls, the section's accountability for the platforms and ammo, and the section's tactical employment under the platoon commander's intent. The Marine Corps's emphasis on NCO leadership at the section-leader tier is institutionally distinct — the SgtMaj's eye on 0331 Sgts is structurally tighter than the equivalent visibility in other branches' machine gun communities. The MEU cycle continues as the structural rhythm. As a section leader Sgt, you're running the machine gun section through PTP workup (~12-15 months) — gunnery progression, MEU-SOC certification training, integration with the BLT's maneuver companies — and deploying afloat on the MEU as the senior MG NCO in the company. The MEU's various mission profiles (TRAP, NEO, embassy reinforcement, MARSOC support, contingency response) all pull the machine gun section into the operational fight at the section-leader tier. The lateral move / B-billet window at Sgt: same options as 0311 Sgts — MARSOC selection (M&S Course at Camp Lejeune is the entry point; the MARSOC training pipeline runs ~7-9 months including the Marine Raider Training Center course at Camp Lejeune; MARSOC Sergeants pursue CSO Operator progression — verify current MARSOC SNCO model against MARADMIN), Reconnaissance (0321 Recon Man via BRC at Coronado, ~9 weeks), drill instructor (DI duty at MCRD Parris Island or San Diego, ~3 years, the DI badge), Marine Security Guard (MSG program at Quantico, embassy postings 12-36 months globally), recruiter (8411 Recruiter MOS via Recruiter School in San Diego, ~6 weeks, 3-year recruiting tour), and the various specialty schools and instructor billets at SOI East/West. The Combat Marksmanship Instructor (CMI) and the senior machine gunner / advanced gunner instructor billets are 0331-specific career-shaping credentials. Verify the current Marine Corps advanced machine gunner course catalog at TECOM — the Corps maintains advanced machine gunner programs that compound for senior-NCO competitiveness at the SSgt board. The reenlistment / EAS math at this rank: 0331 SRB tier and bonus amounts are published in current MARADMIN messages and vary year over year. The career planner conversation at Sgt is structured around the lateral move decision (the biggest career-shaping decision of the rank tier), reenlistment incentive, and the SACO variants. Don't sign without reading the current MARADMIN. The post-service market for 0331 Sgts mirrors the 0311 Sgt market — defense contracting, federal LE (Border Patrol, US Marshals, FBI tactical, ATF), and the long tail of security-services firms hire Marine NCOs with infantry/heavy-weapons experience and clearance. The 0331's specific platform skills are less directly portable than some MOSes, but the Marine NCO leadership package + combat experience + clearance is the load-bearing post-service value.
Career Arc
  • 01Cpl → Sgt pin-on via cutting score under MCO P1400.32D.
  • 02Machine gun section leader assumption — multiple M240 teams or heavy MG vehicle crews.
  • 03Sergeants Course PME completion (in-residence or CDET).
  • 04MEU PTP workup → MEU deployment afloat as section leader.
  • 05Lateral move / B-billet window: MARSOC (M&S Course), Recon (BRC), DI duty, MSG, recruiter (8411).
  • 06Career Course PME — preparation for SSgt centralized selection.
  • 07Centralized SNCO selection board for SSgt (E-6) — paper-record review.
Common Screwups
  • ×Phoning the section leader role. The Marine machine gun section's effectiveness is the Sgt's effectiveness; SNCOs and CO read it on every live-fire range and FTX rotation.
  • ×Missing Sergeants Course / Career Course PME. The SSgt board reads the PME record; missed gates are visible and there's no recovery within a board cycle.
  • ×NJP / DUI / fraternization — separation under MARCORSEPMAN, clearance issues, lateral move and SSgt selection foreclosed.
  • ×FITREP drift. The Marine FITREP system weights heavily in the SSgt selection board; sloppy narratives or weak reporting-senior ratings propagate and compound.
  • ×Underestimating the lateral move decision. MARSOC, Recon, MSG, DI, recruiter — each is materially career-shaping and time-constrained; the window narrows past mid-Sgt.

A Day in the Life

  • 0500-0530Wake. Phone check for the platoon group chat — any liberty incidents over the weekend, any Marine in the brig, any 0400 alert formation. None? Good. PT uniform on, water bottle filled, head to the company area.
  • 0530-0545PT formation in the company area. You take accountability for your gun squad (you + three Cpls + nine to twelve LCpls/PFCs across the three gun teams, depending on current TO&E), report to the weapons platoon sergeant (SSgt). Your team leaders report up through you. Missing Marine = your problem first.
  • 0545-0700Unit PT. The 0331 community runs harder than the line rifle platoons on hump days because the gun weight rides the difference. The gun squad you lead sets the pace as the example — you ruck at the front with the gun loaded, you set the run pace, you set the MCMAP mat work. Wednesdays the platoon humps together; Thursdays may be the squad-led PT block where you build the plan. The platoon sergeant watches whether your gun squad holds pace and ruck weight under the gun load.
  • 0700-0830Hygiene, chow, change into utilities. Pre-walk the gun squad area before morning formation — your Cpls should not be finding what you should have caught. The good Sgt walks every gun team's rack and locker space at least once a week.
  • 0830Morning colors / first work formation. Platoon sergeant gives the day's tasking and the week's training schedule updates. You confirm gun squad accountability and uniform; you brief your three Cpl team leaders on the day's priorities of work, and they brief their teams. Sensitive items inventory — guns, T&Es, tripods, spare barrels, crew-served optics by serial — signed.
  • 0900-1130Work day — gun-squad-level training (collective task rehearsal, multi-gun-team FPF orientation, displacement coordination, gun squad live-fire range coverage), range coverage as the squad leader, working party as the senior NCO on the manifest, or company-level event. You are running the gun squad's rep, not the team-leader running it under you.
  • 1130-1300Chow. As an NCO you sit with the other Sgts and the SSgts; your Cpls sit with the Cpls; your LCpls sit with the LCpls. The chow hall organization is the visible chain of command.
  • 1300-1500Afternoon work — finish whatever the morning task did not close. FitRep input cycles for your three Cpls (you write the Section A, the weapons platoon commander writes the attributes, the company commander reviews). Counseling sessions with your Cpls — monthly Pro/Con sit-down at minimum, formal page-11 if the situation warrants. PME study time if you are reading for Career Course or Machine Gun Section Leader Course.
  • 1500-1630Final formation. Platoon sergeant gives the next day's plan; you brief your gun squad. Sensitive items (guns, T&Es, tripods, spare barrels, NVGs, optics, comm gear, crypto) checked back into the armory; your Cpls run the gun team counts, you sign the gun-squad-level count. You hand each Cpl a 3x5 card with tomorrow's priorities.
  • 1630Liberty call (if the company is on normal schedule). Field problems, ranges, range coverage, working parties, and guard duty break this hour.
  • 1700-2000Personal time. If you are married and live off-base, family time. If you are in the barracks or single off-base, gym for a second session, PME study time, financial / family admin. The good Sgt protects his home time and uses personal time for personal growth — Career Course coursework, civilian college courses through Tuition Assistance, NCO leadership reading.
  • 2000-2200If a Marine in your gun squad called you about a problem — financial, marital, legal, family, medical — you are on the phone or driving over. The gun squad leader's after-hours job starts here. The Sgt who answers the phone and shows up is the Sgt the gun squad trusts with anything that matters.
  • 2200Lights out. Tomorrow starts at 0500.
  • FTX / ITX at MCAGCC Twentynine PalmsClock breaks. Squad-led gun drills during the day, platoon-level lanes when the platoon sergeant runs them, sleep in shifts in the patrol base. You are awake before stand-to at 0500, your gun squad's sector is your responsibility through evening stand-to, and you sleep when the platoon sergeant rotates you out. A 21-day ITX rotation feels like 45 — and the OC/T at MAGTFTC is reading every gun squad leader in the company. Multi-gun-team integration (interlocking sectors of fire, coordinated FPF orientation, displacement under the platoon commander's scheme) is the squad-leader-tour level of evaluation.
  • MEU deployment afloat (6-7 months)Gun squad leader on the BLT (Battalion Landing Team) embarked on amphibious shipping (LHD/LPD/LSD). MEU-SOC training days, port visits when granted, contingency response posture days. You integrate with the Navy ARG, run gun-squad-level training on the limited shipboard space, and brief the weapons platoon commander on gun squad readiness daily during the contingency posture windows. You are also the visible Marine NCO face of the gun squad during shore liberty and contingency operations — the SgtMaj of the MEU is watching.

Weekly Cadence

The Mon-Fri rhythm at Sgt in the 0331 community runs on the weapons platoon training schedule and the gun squad's read of where the squad needs work. Monday is the heaviest planning day for the squad leader — the platoon sergeant puts out the week's training schedule at Friday's release, but Monday morning is when you find out what got cut, what got added, and what additional duty the company gunny just remembered. You spend the morning in pre-walk mode for whatever the gun squad is doing this week; the afternoon is the first counseling slot for any Cpl who needed a Monday Pro/Con sit-down or a FitRep input conversation. Tuesday through Thursday is the rhythm of gun squad training. Squad-level collective task rehearsals during shop time — multi-gun-team FPF orientation rehearsal, sectors of fire interlock across the section's training positions, gun squad displacement coordination, ammo and barrel rotation drills under sustained-fire scenarios, gun squad live-fire rehearsals — rehearsed with the three Cpl team leaders running their teams' pieces and you running the gun-squad-level integration. Each Cpl runs his gun team's portion of the lane; you supervise, AAR honestly, and run the lane again. MCMAP sustainment on the platoon's mat day. TCCC drills with the platoon's corpsman. The platoon sergeant pulls the gun squad for platoon lanes once the squad has rehearsed cleanly; the company gunny pulls the platoon for company lanes once the platoon has rehearsed cleanly. The good gun squad leader runs his squad's training the way the platoon sergeant runs his platoon's — calendar-driven, sustainment-tracked, AAR-honest. The week's other rhythm is the NCO admin layer that the platoon sergeant and company gunny push down. FitRep input cycles for your three Cpls run on the Marine Corps FitRep schedule (verify current revision on Marines.mil). Pro/Con marks monthly on each Marine. Formal page-11 entries when discipline issues arise. Field gear inventory for upcoming workup and MEU events — gun bag inventory by gun, T&E pouch inventory, spare barrel inventory, optics inventory, crew-served comm inventory. Training records signed off in the unit training system. Career Course coursework runs alongside — distance education through CDET or in-residence at the regional NCO academy. The MEU PTP workup compresses this rhythm — when the battalion is in the workup cycle, the family conversation about why you were not home for dinner three nights this week is real, and the good Sgt protects his home time as carefully as he protects the squad's training time. Field rotations (MCAGCC Twentynine Palms ITX, MWTC Bridgeport, JWTC Okinawa during UDP, MEU PTP) collapse garrison-time entirely — garrison-time becomes sleep, range coverage, and the documentation you owe before the next field problem starts.

Key Skills — How to Drill Each

  1. 01
    Develop and brief a gun squad scheme of fires the platoon commander does not have to rewrite — gun positions, sectors of fire, FPF orientation, grazing / plunging fire plan, displacement and resupply, integration with the supported rifle squads.
    Build the scheme on the platoon's terrain model first, then on a map sheet with overlays, then in the SMEAC format the platoon commander quotes back. The gun squad's contribution to the company's scheme is the base of fire — sectors of fire interlocked across the multiple gun teams, FPF orientation locked against the most likely enemy avenue of approach, grazing fire planned to 600m out, plunging fire planned for elevated positions or terrain-shaped beaten zones, displacement plan that gets the section out of the position before counter-battery or maneuver counter-attack, resupply plan that gets ammo to the teams during the fight. The platoon commander who has confidence in his squad leaders' schemes is the platoon commander who delegates — and the Sgt who earns that delegation is the Sgt the SSgt selection board reads differently years later. Brief in 200 specific words rather than 400 generic ones; the platoon commander reads the difference.
  2. 02
    Run a gun squad live-fire as the squad leader — ORM, surface danger zones (SDZ) accounting for the multiple gun teams' beaten zones, MEDEVAC plan, ammo accountability, barrel rotation plan — to the NAVMC 3500.44 collective standard.
    Gun squad live-fire is the test of squad-leader competence. Run the Operational Risk Management (ORM) worksheet honestly — known hazards across the multiple gun teams (the SDZ math is geometrically larger for a squad than for a single team), weather and visibility constraints, fatigue management during sustained fire, ammo and barrel rotation cycles, communications failure contingencies. Rehearse the squad dry, then blank, then live, then graded. The MEDEVAC plan is named — primary 9-line route, secondary, CCP location, marking method, casualty triage across multiple teams. Ammo accountability is the platoon sergeant's first check after the lane; have the count clean across all three teams before he asks. Barrel rotation across teams: hot barrels rotated out per the operator's manual sustained-fire cadence, spare barrels staged at the section's logistics point. The Sgt who runs a clean gun squad live-fire is the Sgt the company commander gives the harder lane to next.
  3. 03
    Write a clean Section A on FitReps for your three Cpl team leaders — observed behavior, action-result-impact, no inflation the reporting senior cannot defend at battalion FitRep review.
    FitRep Section A under MCO 1610.7 (verify current revision on Marines.mil) is the narrative input that drives the attribute marks and the relative value. Write in observed-behavior terms — what the Cpl did, in what context, with what measurable result. The reporting senior (typically the weapons platoon commander) builds the attribute rationale off your Section A; the reviewing officer (typically the company commander) reads it against every other Sgt's input in the company. Inflated narratives ('best Cpl in the battalion') without specific action-result-impact backing do not survive the battalion FitRep review. The good Sgt writes Section A in 200 specific words: name the gun team's live-fire range performance, name the Machine Gun Leader Course graduation, name the Marines pinned during the rating period under the Cpl's mentorship. The platoon commander calls you at the end of the rating period to ask about specific Cpls because your Section A actually describes what each Marine did.
  4. 04
    Run a gun squad through MCCRE-graded lanes and recover from a thumping AAR without losing the squad on the way out.
    MCCRE (Marine Corps Combat Readiness Evaluation) is the unit-level collective evaluation that grades the squad and platoon against NAVMC 3500.44 collective standards by external evaluators (OC/Ts at MAGTFTC Twentynine Palms during ITX, evaluators from the MEF level for MEU-SOC certification). The gun squad will fail a lane during the workup — that is not the question. The question is what the squad looks like in the AAR and what the squad looks like on the next lane. The good squad leader runs the AAR honestly — what we did, what we missed, what we change for the next iteration. The bad squad leader gets defensive or shifts blame. The platoon sergeant reads the recovery as the leadership signal. Gun squads that recover hard and execute better on the second iteration are the gun squads the platoon commander trusts on the MEU and the SSgt selection board reads at the squad-leader-tour level.
  5. 05
    Mentor your three Cpl team leaders into Sergeants Course-ready and Machine Gun Section Leader Course-graduate candidates — team leadership, FitRep prep, composite score management, voluntary school slot push.
    Your three Cpls are your bench. Each of them is on a Sergeants Course timeline, a cutting-score build, a team-leader-to-section-leader development arc — and your job is to compress the timeline cleanly. Monthly counseling sessions on composite score (where they are, where the cut sits, what they can do this quarter to close the gap). PME slot push through the platoon sergeant — Corporals Course done, Sergeants Course slated, Machine Gun Leader Course attended or slotted. Live-fire reps where the Cpl runs the team's portion of the lane and you supervise. MCMAP belt timeline — Green to Brown to Black. Voluntary schools — CMC, MCMAP instructor, Machine Gun Section Leader Course early seat if pulled. The Sgt who pins two or three of his Cpls to Sgt during his squad-leader tour is the Sgt the SgtMaj remembers — and the SgtMaj's read carries to the SSgt selection board.
  6. 06
    Walk a Marine through a financial problem (predatory lender, garnishment, command financial specialist referral) without making it the platoon sergeant's problem first.
    MCCS (Marine Corps Community Services) runs Personal Financial Management Program (PFMP) counseling at every installation, no cost. The Command Financial Specialist (CFS) at the unit level can stop a garnishment with the right paperwork. Legal Assistance at the base law center will review a predatory loan and write a cease-and-desist for free. You are not solving the Marine's debt — you are routing him to the offices that can. Keep the building numbers and the CFS's phone number on your phone. The squad leader who routes financial problems cleanly is the squad leader the platoon sergeant does not have to escalate around. The same routing logic applies to SAPR (Marine Corps Sexual Assault Prevention and Response under MCO 5354.1 — verify current revision), Behavioral Health referrals, chaplain referrals, EO complaints under MCO 1000.9, and the various command-team referrals the Sgt is positioned to make cleanly.

Manuals & References — What Chapters Matter

  • The current MCRP 3-15-series machine gun and heavy weapons employment manual
    Own this cover to cover at the Sgt rank — the platoon sergeant and platoon commander quote it back to you in the squad scheme back-brief. The chapters on multi-gun-team integration, sectors of fire interlock, FPF orientation across multiple teams, grazing vs plunging fire, beaten zone geometry, displacement, and platform-specific employment (M240, M2, MK19) are the spine you brief from and the spine the OC/T evaluator quotes during the MCCRE lane. Verify the current subnumber against the Marine Corps Publications Electronic Library before quoting chapter and verse — the manual numbering has moved across recent revisions.
  • MCRP 3-10A.3 — Marine Rifle Squad and MCRP 3-10A.4 — Marine Rifle Platoon
    The units your gun squad supports and integrates with on every offensive and defensive operation. As a Sgt squad leader you brief and coordinate at the platoon level — the rifle platoon's offensive and defensive doctrine, the rifle squad's tactical control measures, the platoon-level integration of base-of-fire and maneuver. The platoon back-brief is where the squad leader's grasp of platoon doctrine is tested; the Sgt who quotes MCRP 3-10A.4 confidently is the Sgt the platoon commander trusts to run a gun squad on an independent task.
  • MCWP 3-01 — Offensive and Defensive Tactics for the Marine Air-Ground Task Force
    The doctrinal umbrella for how the MAGTF fights. As a Sgt you are running a gun squad inside a battalion that operates at MAGTF level on a MEU; understanding the bigger picture changes how you brief and how you execute. The chapters on the rifle platoon and rifle company in offensive and defensive operations are the platoon commander's reading list — match it.
  • NAVMC 3500.44 — Infantry Training and Readiness Manual (Sgt / gun-squad-level collective tasks)
    The T&R Manual is the source of every collective task your gun squad is evaluated against. At Sgt, you are evaluated on 2000-level squad collective tasks and you sign off on 1000-level individual tasks for your Marines. Print the gun-squad-level collective tasks chapter and walk it down with the platoon sergeant during your first 30 days as a squad leader. The MCCRE evaluators quote this manual on every lane.
  • MCO 1610.7 — Performance Evaluation System
    You write FitReps now under MCO 1610.7 — not just receive them. The FitRep policy chapter, the Section A narrative input chapter, the attribute marks rubric, the reporting senior and reviewing officer responsibilities — all of it is your reading list. Verify the current revision on Marines.mil before quoting chapter and verse; the system has been updated across recent revisions. The good Sgt understands the relative-value math and writes Section A input that survives the battalion FitRep review and reads at the SSgt selection board years later.
  • MCO 1400.32 — Marine Corps Promotion Manual
    The composite score, cutting score, and board eligibility framework for both the Cpl/Sgt cutting-score system and the SNCO selection-board system. The Sgt who understands the SSgt selection board's relative-value mechanic — and who is building a FitRep profile aligned to that mechanic — is the Sgt who is competitive for SSgt selection three or four years out. Read the SSgt board mechanics chapter carefully; verify the current revision before quoting. Pull the current MARADMIN for SSgt selection rates.

Standards — How to Hit Each

  • Sergeants Course graduate — required PME for Sgt promotion (verify against current MCO/MARADMIN); Career Course slot scheduled on the SSgt timeline.
    Sergeants Course is delivered at regional Marine Corps NCO academies (Camp Lejeune, Camp Pendleton, Camp Foster Okinawa, etc.) in-residence, or via CDET non-resident. In-residence is materially better — both for the rigor and for the network of Sgts you meet from across the Corps. Pull the in-residence slot 90 days out through the platoon sergeant. Career Course is the next PME tier — the SSgt selection board reads PME completion, and the Sgt who has Career Course locked in 12-18 months before the SSgt board is the Sgt who is competitive. Schedule both with the platoon sergeant and the company gunny.
  • Machine Gun Section Leader Course graduate (or slated) — the next billet expects it before you walk into it.
    The Machine Gun Section Leader Course is the 0331-specific advanced school at the Sgt/SSgt rank — typically delivered as a TECOM-managed course (verify the current course name, location, prerequisites, and POI against the Marine Corps's course catalog at TECOM; the course has moved across revisions). The credential is the visible technical-depth signal the SNCO leadership reads at the SSgt selection board. Slot push through the platoon sergeant and the company gunny; the GySgt will note attendance. The Sgt who has the credential is the Sgt the SSgt selection board reads cleanly; the Sgt who didn't pursue it is the Sgt who has to make up the differential elsewhere.
  • Brown Belt MCMAP minimum; Black Belt is what the company gunny notes on the next FitRep.
    MCMAP belt progression — Gray, Green, Brown, Black — under MCO 1500.54 is the visible signal of self-discipline that the SNCOs read. Brown Belt is the bar at Sgt; Black Belt is what the company gunny notes on the next FitRep and what the SSgt selection board reads. Schedule the Brown Belt tape with the platoon's senior MCMAP instructor; build a Black Belt timeline with the company gunny. The Sgt who has Black Belt before the SSgt board is the Sgt whose composite reads cleanly. The gun community's emphasis on physical conditioning makes MCMAP progression a natural complement to the PFT/CFT discipline already required by the gun's weight.
  • 1st-Class PFT and 1st-Class CFT under MCO 6100.13; your gun squad average is watched and reported, and the gun does not forgive a 2nd-Class squad leader.
    At the Sgt rank you are not just hitting 1st-Class for yourself — you are hitting it as the squad's standard-bearer. The platoon sergeant and company gunny see the squad's PFT/CFT pass rate on the unit health-of-the-force report; a gun squad with a Sgt who hits 1st-Class and a sub-1st-Class squad pass rate is the squad the SgtMaj asks about. Lift heavy three days a week, run intervals two days a week, plate-carrier-rucks (with the gun and tripod loaded) once a week, and the squad pulls behind you. Below 1st-Class as a squad leader, the SSgt selection board reads it.
  • Squad MCCRE / pre-deployment evaluation rated at the unit standard or above — the platoon commander's next FitRep depends on it.
    MCCRE rating is a unit-collective evaluation graded against NAVMC 3500.44 collective standards by external evaluators (OC/Ts from MAGTFTC at Twentynine Palms during ITX, evaluators from the appropriate Marine Expeditionary Force level for MEU-SOC certification). The gun squad leader is the proximate cause of the gun squad's MCCRE rating. Build the squad's training plan with the platoon sergeant 90-120 days out from the evaluation; rehearse the collective tasks dry, blank, live, and graded; AAR honestly and execute better on the next iteration. A clean MCCRE rating travels — the platoon commander writes you a clean FitRep, the company commander reads the rating in the battalion review, and the SSgt selection board reads it years later in your record.

Technical Mistakes — Concrete Consequences

  • Verbal counseling only — no page-11 entry, no formal counseling sheet on file.
    If it is not in writing — page-11 entry under the current Marine Corps administrative policy, or formal counseling on the unit's counseling template — it did not happen and the company commander cannot defend you when it matters. When a Marine appeals an Article 15 or files an IG complaint, the chain's first move is to pull every counseling on file. A verbal counseling you swear you gave is invisible in the legal file; the Marine's lawyer (or the IG investigator) will use the gap to argue you fabricated the standard after the fact. Five minutes typing a page-11 entry is a year of legal defense for you and your company commander.
  • Letting a gun team smoke the platoon sergeant's sensitive-items count because you did not pre-inspect on Sunday — serialized gun, T&E, optic, and tripod all get inventoried by serial number, and one missing line item eats the company training calendar for a week.
    The platoon sergeant's read on the new gun squad leader is set in the first 30-60 days. A gun squad that fails its first sensitive-items count without your pre-walk gets attached to your name for the rest of the workup, and the platoon sergeant's read of you closes within a quarter. The MEU manifest does not include gun squad leaders with sensitive-items incidents on the workup record. The gun community's accountability burden is geometrically larger than the rifle community's — guns, T&Es, tripods, spare barrels, optics (thermals, day optics, range finders), and crew-served comm gear all sign by serial. Pre-walk the count on Sunday afternoon; sign off on each Cpl's serialized gear before the platoon sergeant's check on Monday morning.
  • Doing the work yourself instead of teaching the Cpl team leader to do it.
    When you leave for Sergeants Course or Career Course for two weeks, the squad you trained with workarounds collapses. The Cpl who never ran a PCI in front of the platoon sergeant has to run it cold on the next field problem. The Cpl who never built a range card under the platoon commander's eye has to build it cold on the next defensive lane. The platoon sergeant sees your gun squad is the platoon's weakest and the read sticks. The good gun squad leader trains his Cpls to be ready to take the squad — the bad squad leader makes himself indispensable and then the squad fails when he is gone.
  • Hiding a SAPR, EO, or self-harm-ideation issue from the chain to 'protect the Marine.'
    Sexual Assault Prevention and Response (SAPR) under MCO 5354.1 and Equal Opportunity under MCO 1000.9 require defined reporting timelines (verify current revisions on Marines.mil). Hiding an incident to 'protect the Marine' violates the order, exposes the chain to negligent-supervision liability, and almost always ends with the Marine in worse shape and the Sgt in front of the company commander explaining the gap. The Marine is better served by the system than by your discretion — the SAPR Victim Advocate, the Behavioral Health team at the Branch Medical Clinic, the chaplain, and the SARC (Sexual Assault Response Coordinator) exist for exactly this. The 24-hour and 72-hour reporting windows are non-negotiable.
  • Going around the platoon sergeant to the company gunny or 1stSgt with a squad-internal problem.
    The platoon sergeant finds out within a week that you went around him. The company gunny will tell him; the 1stSgt will tell him; sometimes the SgtMaj will tell him. The platoon sergeant stops trusting you with anything that matters; the company gunny loses confidence in the platoon sergeant's grip; and the platoon's command climate fractures along the gap you created. The chain runs through your platoon sergeant for a reason. The fix is one apology, in his office, with the door closed — and a year of rebuilding trust.

Career Decisions at This Rank

  • Lateral move pipeline at Sgt — MARSOC A&S → 0372 CSO, Recon (BRC → 0321), current sniper community, or stay 0331 gun squad leader
    At Sgt the window for the major lateral pipelines is open but narrowing. MARSOC A&S at Camp Lejeune is the entry point for the 0372 Critical Skills Operator pipeline; the MARSOC training pipeline runs ~7-9 months total including the Marine Raider Training Center course at Camp Lejeune. MARSOC Sgts have a meaningfully different career arc than line infantry Sgts — different OPTEMPO, different community, different post-service market. Recon (0321 Recon Man via BRC at Coronado, ~9 weeks) is open at Sgt; the Recon Sgt path leads to Reconnaissance Battalion or Force Reconnaissance Company assignments. The current Marine Corps sniper / advanced infantry community has gone through major restructuring (verify against current MARADMIN — the 0317 MOS and SSBC structure have moved). The honest math at Sgt: each of these pipelines is materially career-shaping, and the time investment compresses against the Career Course timeline and the SSgt selection board read. Stay 0331 and the gun-squad-leader-to-section-leader arc is the default; pivot to MARSOC, Recon, or the current sniper community and the SOF career arc opens. Past mid-Sgt the screening windows close.
  • B-billet pipeline at Sgt — DI duty at MCRD, MSG at Quantico, Recruiter School in San Diego
    B-billet (special duty assignment) at Sgt is a different math than at Cpl. Drill Instructor (DI) duty at MCRD Parris Island or San Diego is ~3 years; the DI tour identifier is a known check at the SSgt board and the GySgt board, and many SgtMajs came up through DI duty as Sgts. Marine Security Guard (MSG) at Quantico opens embassy postings — fundamentally different operational environment, professional Marine NCO at U.S. embassies globally, with the corresponding career-broadening read. Recruiter School in San Diego (~6 weeks) opens a recruiter tour at a recruiting station (the 8411 Recruiter MOS) — small-civilian-community billet where you are the Marine Corps to your neighbors. Each B-billet ages you fast, pays an SDA-equivalent bonus, and is visible at the SSgt board. The cost: family quality-of-life during a DI tour is brutal; recruiter tours move you to a small civilian community far from a base. Talk to Marines who have done the tour before you volunteer.
  • Career Course in-residence versus distance education through CDET
    Career Course is the PME tier between Sergeants Course and the SNCO Academy at Camp Geiger (verify current PME mapping against MCO 1500.59 and current MARADMIN — the Marine Corps PME structure has been updated across recent revisions). The in-residence variant is delivered at regional NCO academies and is materially more rigorous than CDET. The SSgt selection board reads PME completion; the Sgt who has Career Course locked in 12-18 months before the SSgt board is the Sgt who is competitive. In-residence is the preferred option if the slot drops and the family math supports it; CDET is the option that works around deployment schedules. Talk to the platoon sergeant and the company gunny about timing.
  • Reenlistment at Sgt — sign for the bonus, indef, or EAS
    Reenlistment math at Sgt is different from Cpl. SRB tier and bonus amounts for 0331 Sgts are published in current MARADMIN messages and vary year over year — pull the current MARADMIN before you sit with the career planner. The re-up options usually break into: indef reenlistment to compete for SSgt selection, lateral move contract (MARSOC, Recon, B-billet), station-of-choice for the next tour, school-of-choice option, or SACO (Special Assignment Career Option) variants. The honest math: Sgts who EAS at first reenlistment leave significant SSgt-trajectory potential on the table; Sgts who reenlist to chase the bonus without a clear billet plan end up underwater on the contract. The senior career planner conversation is structured — show up with a plan, not a question.
  • Commissioning at Sgt — MECEP, ECP, or stay enlisted to compete for SSgt
    For Sgts who have built college credits through Tuition Assistance and CCAF or who have a bachelor's degree in hand, the Marine Enlisted Commissioning Education Program (MECEP) and the Enlisted Commissioning Program (ECP) remain open. MECEP keeps you in active-duty pay and benefits while you complete the degree at a participating university; ECP is the direct commission for Sgts with a bachelor's already in hand. The honest test at Sgt: are you better at executing missions or at building systems, writing policy, and running staff work? Sgts who love being squad leaders make average platoon commanders. Sgts who keep asking 'why are we doing this the way we are doing this' make excellent platoon commanders and company commanders. Talk to the platoon commander and the company commander — the officer chain's read is the leading indicator of whether to package. Sgts also have the option to stay enlisted, compete for SSgt, and build the senior-NCO trajectory that runs to SgtMaj.

How the Seat Varies by Unit Type

  • Standard infantry battalion weapons platoon
    The default 0331 Sgt assignment — gun squad leader in the machine gun section of a rifle company's weapons platoon, running three M240 gun teams under three Cpl team leaders. The rhythm is MEU PTP workup → MEU deployment afloat → reset, with FTX rotations to MCAGCC Twentynine Palms (ITX), MWTC Bridgeport for mountain warfare training, JWTC Okinawa during UDP deployments, or local training areas. The weapons platoon sergeant is a SSgt, the company gunny is a GySgt, the 1stSgt of the company is reading FitReps on every Sgt in the company, and the SgtMaj of the battalion knows the gun squad leaders by name and reputation within 90 days.
  • Marine Expeditionary Unit (MEU) BLT — afloat MG section
    Gun squad leader on the Battalion Landing Team embarked on amphibious shipping (LHD/LPD/LSD). 6-7 month MEU deployment with the Navy ARG. MEU-SOC mission profiles (TRAP, NEO, VBSS, raid operations, mechanized raid, helo raid) define the deployment, and the Sgt gun squad leader runs gun-squad-level execution of those mission profiles. The MEU is the formative operational experience for the 0331 Sgt — Sgts who deploy MEU as gun squad leaders come back with the operational rep that defines the SSgt selection board read. Port visits, contingency response posture days, and the daily integration with the Navy ARG fill out the deployment rhythm. The multi-gun-team integration on the MEU-SOC mission profiles is the section-leader-tour level of gun-squad operational experience.
  • Unit Deployment Program (UDP) — Okinawa
    Battalions from Camp Lejeune and Camp Pendleton rotate to Okinawa (Camp Schwab, Camp Hansen, Camp Foster) for UDP cycles, typically 6 months. Land-based forward-deployed under III MEF, training at the Jungle Warfare Training Center on Okinawa, partnering with allied forces in the Indo-Pacific (Korean Marines, Japanese Ground Self-Defense Force, Philippine Marines, Australian Defence Force, etc.), and standing contingency response postures. Unaccompanied tour for most Marines — the marriage math is different from a CONUS-based assignment. The Sgt who runs a gun squad through UDP gains different operational experience than the MEU Sgt — partnership training, regional engagement, jungle and amphibious operations at scale.
  • Weapons Company / heavy machine gun section
    Some battalions structure their heavy weapons (M2 .50 cal, MK19 40mm) at the battalion weapons company level rather than the rifle-company weapons platoon level — depending on the current TO&E (verify against current MCO and MARADMIN; Force Design has moved this structure across recent updates). Sgts assigned to a battalion-level heavy weapons section lead heavy-MG sections (M2 / MK19 vehicle-mounted crews on JLTV, MRZR, or vehicle integration). The heavy MG community has a different tactical employment profile — area suppression, vehicle integration, convoy security — and the Sgt's craft skills and FitRep narratives develop along the heavy-MG specialization. The technical depth signals are different: M2 headspace and timing mastery across multiple guns, MK19 belt-link and fuze handling, mounted gunnery integration with vehicle commanders.
  • Lateral pipelines (0311 conversion, 0317 Recon, 0321 Recon/MARSOC 0372 CSO)
    Sgts who screen for Recon (BRC at Coronado, ~9 weeks → 0321 Recon Man MOS assignment in Reconnaissance Battalion or Force Reconnaissance Company), MARSOC (A&S at Camp Lejeune → Marine Raider Training Center course → 0372 Critical Skills Operator MOS assignment to a Marine Raider Battalion), or the current Marine Corps sniper community (verify current MOS structure against MARADMIN — the 0317 MOS and SSBC have been restructured across recent updates) take a fundamentally different career arc. The training pipelines are materially harder than line infantry; OPTEMPO is higher; the communities are smaller and more institutionally insular. 0311 lateral conversion is a separate fork — the rifle squad and gun squad communities converge at SSgt rank under the senior infantry NCO model (verify against current MCO — the 03XX occfield convergence has moved across recent revisions), and converting at Sgt simply changes which squad you live in. Sgts who screen at this rank typically come up with the skill base, the run times, the ruck times, and the platoon sergeant's recommendation already in place. Past mid-Sgt the screening windows narrow.

What Good Looks Like at This Rank

The good Sgt gun squad leader is the squad leader the platoon sergeant gives the worst Marine in the company to, because that Marine comes back a Marine instead of a paperwork problem. He does not yell at his Cpls in front of the squad. He does not make examples in front of the formation. He sits with the Marine in his office at 1900 on a Thursday and writes a clean page-11 entry that says exactly what the Marine will do on Monday at 0530, signs it, has the Marine sign it, and saves it to the unit's counseling file. By Monday at 0531 the Marine is in formation in the right uniform, and the Sgt has the paperwork to support whatever consequence follows if he is not. His gun squad passes the company's MCCRE lanes at the unit standard or above, not because his Marines are smarter than the other gun squads' Marines, but because he spends the 90 days before the workup running his own terrain-model rehearsals on Wednesday nights, walking range cards with each of his Cpl team leaders on Saturday mornings, and running gun-squad radio comm drills in the company parking lot at 1800. The platoon commander can be at the company office writing his next OPORD and the gun squad executes the platoon sergeant's plan anyway, because the Sgt has rehearsed his Mon-Fri rhythm to the point that nothing rides on his presence. His three Cpls are Machine Gun Leader Course graduates, his gun teams' range cards are the ones the platoon commander signs without redraw, his gun squad's sensitive-items count has never tripped a 1stSgt's check, and the FPF orientation his squad set on the last live-fire range is the FPF the company commander briefed at regiment. The platoon sergeant's read on his future-SSgt potential is set by month nine. The Career Course packet is built before the slot drops. The MEU manifest assigns him the heaviest gun squad in the BLT because the company gunny has read his Pro/Con marks and his FitRep input. The FitReps on his three Cpls are clean — observed behavior, action-result-impact, no inflation — and the reporting senior (the weapons platoon commander) calls him at the end of the rating period to ask about specific Cpls because his Section A actually describes what each Marine did. That trust is the differentiator between a Sgt who is competitive at the SSgt selection board and a Sgt who sits in zone for an extra cycle. The SgtMaj of the battalion knows his name within the first six months — and the SgtMaj's read of which Sgts are future SSgts, future GySgts, and future SgtMajs is the implicit input on every assignment slate. He has Brown Belt MCMAP rolling into Black, 1st-Class PFT and CFT, voluntary CMI / Machine Gun Section Leader Course credentials, and the kind of clean conduct record the SSgt board reads as competitive.

Preview — The Next Rank

SSgt (E-6) in the 0331 community is the weapons platoon section leader rank — the senior NCO of a machine gun section (multiple gun squads of multiple gun teams each, depending on the current TO&E and Force Design), sometimes paired with mortars (0341) and assaultmen (0351) under the same SSgt — or the platoon sergeant of a 30-45 Marine weapons platoon. The Marine Corps's weapons platoon section leader slot is one of the most consequential billets in the Corps's enlisted infantry structure: you run the section's or platoon's enlisted side (training, evaluations, schools, promotions, MCMAP belt progression, discipline, equipment accountability, family readiness) for a population whose job is heavy weapons employment and whose gear list is longer than a rifle platoon's by a factor of three. The promotion math to SSgt is structurally different from Sgt promotion. Sgt-to-SSgt runs through the Marine Corps's centralized selection board for the SNCO ranks under MCO 1400.32. The SSgt selection board reads your full record — FitReps with relative-value placement, composite scores, awards, education credits, PME completion (Sergeants Course required, Career Course preferred), conduct/proficiency marks, and the various inputs to the SNCO competitive package. Unlike the cutting-score system for Cpl and Sgt, SNCO advancement is paper-record selection-board based — the read is the read. The differentiator on the SSgt selection board is the FitRep relative-value profile you build at Sgt (gun squad leader who runs clean MCCRE lanes, writes clean Cpl FitReps, and earns 'must select' or equivalent narrative input from the reporting senior) plus the PME stack (Sergeants Course → Career Course) plus the visible squad-leader performance during the workup and the MEU plus the 0331-specific technical credentials (Machine Gun Section Leader Course attended). Job content at SSgt operates at company and battalion level. The company gunny (GySgt) and the CO know your name and read your work weekly. The S-3 schedules training around what your platoon can support. The BSgtMaj is reading your FitRep against every other weapons platoon sergeant in the battalion. You are running the platoon training calendar in concert with the company training calendar, mentoring three Sgts into SSgt-selection-board-ready candidates, writing FitReps the reporting senior can defend at battalion FitRep review, running platoon-level live-fire and MCCRE events, and acting as the company gunny in his absence. The SSgt-to-GySgt selection board is the next career hurdle and it is FitRep-driven — one weak cycle moves the timeline by years. Plan the Career Course completion 12-18 months before the SSgt board; plan the SNCO Academy Advanced Course (Career Course at SNCO Academy at Camp Geiger) on the GySgt timeline. The lateral move and B-billet decisions you made at Sgt are now compounding into the SSgt assignment slate, and the 0331 → 0311 / 0369 convergence question becomes live — the senior infantry NCO career pool is shared, and the MMPB monitor will ask.
FAQ

0331 E5 — Frequently Asked Questions

Q01What does a E5 0331 (Machine Gunner) actually do?
You run a machine gun squad in the weapons platoon — three M240 gun teams, sometimes attached to a rifle company in support, sometimes consolidated under the weapons platoon for FPF and defensive missions — and you are responsible for your Cpls' training, your Marines' equipment, their families, and their careers.
Q02What's the most important thing to know as a E5 0331?
Sergeant 0331 is the machine gun section leader rank — typically the senior NCO running the company weapons platoon's machine gun section (multiple M240 teams), or the senior NCO in a battalion-level heavy weapons section (M2 .50 cal / MK19 vehicle-mounted crews).
Q03What does a typical day look like for a E5 0331?
Time-blocked day at the E5 0331 rank tier: 0500-0530 Wake. Phone check for the platoon group chat — any liberty incidents over the weekend, any Marine in the brig, any 0400 alert formation. None? Good. PT uniform on, water bottle filled, head to the company area, 0530-0545 PT formation in the company area. You take accountability for your gun squad (you + three Cpls + nine to twelve LCpls/PFCs across the three gun teams, depending on current TO&E), report to the weapons platoon sergeant (SSgt). Your team leaders report up through you. Missing Marine = your problem first, 0545-0700 Unit PT.…
Q04What mistakes get E5 0331 soldiers fired or relieved?
Phoning the section leader role. The Marine machine gun section's effectiveness is the Sgt's effectiveness; SNCOs and CO read it on every live-fire range and FTX rotation; Missing Sergeants Course / Career Course PME. The SSgt board reads the PME record; missed gates are visible and there's no recovery within a board cycle; NJP / DUI / fraternization — separation under MARCORSEPMAN, clearance issues, lateral move and SSgt selection foreclosed
Q05What career decisions matter most at the E5 0331 rank tier?
Lateral move pipeline at Sgt — MARSOC A&S → 0372 CSO, Recon (BRC → 0321), current sniper community, or stay 0331 gun squad leader — At Sgt the window for the major lateral pipelines is open but narrowing. MARSOC A&S at Camp Lejeune is the entry point for the 0372 Critical Skills Operator pipeline; the MARSOC training pipeline runs ~7-9 months total including the Marine Raider Training Center course at Camp Lejeune. MARSOC Sgts have a meaningfully different career arc than line infantry Sgts — different OPTEMPO, different community, different post-service market.…
Q06What's next after E5 for a 0331 (Machine Gunner) in the Marines?
SSgt (E-6) in the 0331 community is the weapons platoon section leader rank — the senior NCO of a machine gun section (multiple gun squads of multiple gun teams each, depending on the current TO&E and Force Design), sometimes paired with mortars (0341) and assaultmen (0351) under the same SSgt — or the platoon sergeant of a 30-45 Marine weapons platoon.
Q07What manuals and regulations does a E5 0331 need to know cold?
The current MCRP 3-15-series machine gun and heavy weapons employment manual (own this manual; the platoon sergeant will quote it back to you).; MCRP 3-10A.3 — Marine Rifle Squad and MCRP 3-10A.4 — Marine Rifle Platoon (you support and integrate with these formations every field op).; MCWP 3-01 — Offensive and Defensive Tactics for the Marine Air-Ground Task Force.

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Published by the Honest MOS Editorial DeskVerified against DoD/.gov sourcesUpdated May 2026Editorial standards