Organisation and operations of a USMC 81mm Mortar platoon in Vietnam

Page Title - US Marine Corps
Grunt Logo - Grunt in Cover
81mm MORTAR SECTION
Submitted by Michael D. Stewart, RVN Aug '66 - Nov '67


Dear Mike,

Hope this letter finds you with the wind to your back, sun in your face, in good health and of fine spirit. Michael Pomakis forwarded your letter to me re: 81mm's.

My name is Michael D. Stewart and if you reviewed Mike's page you have seen some of my pictures posted there thanks to Mike Pomakis. I knew Mike in Viet Nam and though we were assigned to different Companies and duties we are friends and share some common stories, friends and ground. We served, and participated, in many of the same field "OPERATIONS"

I served with the 3rd Battalion, 7th Marine Regiment, 1st Marine Division in Viet Nam from Aug/Sept. '66 to late Nov. '67 and was attached primarily to "Mike" Company as an 81mm mortarman. Hence the nic I use on webtv; mike for the company and 0341 for the military occupational skill code number for mortars.

Well, enough on this. Mike Pomakis tells me you need some help as to the inner workings of a mortar platoon etc. I began as an ammo carrier, worked up through to assistant-gunner/gunner, then I was briefly a forward observer, and then on to Ammo Corporal/Section Leader and worked for both Company and Battalion guns at one time or another.

Marine Corps boot camp was the place where new "MARINES" were assigned their MOS based on test scores received at the time. In my opinion, perhaps not accurate, the USMC was looking for the more educated men and placed them into MOSís accordingly. Remember, most of us were volunteers, had high school educations or less, and the largest number were going to basic grunt (0311) outfits.

After boot we went to ITR (infantry training recruit). There was a second culling there so to speak. The men that couldn't catch on to their assigned MOS were demoted to basic 0311 grunts. Any man that excelled was promoted to a higher 03 position. I will pause a moment here and explain 03.

ALL Marines are basic 03's. We know the business end of all weapons used in the field; 0311=infantry, 0331=60 machine gun, 0341=81/60MM Mortars, 0351=106 Recoilless rifle/L.A.W.S (light assault weapons systems, like a bazooka, but slightly different). Other 03 designations were given to recon teams/snipers depending on the weapon used i.e. modified M-14's or Bolt action 30.06's.

ORGANISATION

Two (02) tubes to a mortar section. One (01) sections to a Company. Four (04) Companies to a Battalion + H&S Company (Hospital-Hotel & Support)

Structure: 81MM mortar platoon

  • Two (2) tubes
  • 1 x Section Leader (Cpl E-4 or Sgt E-5). Official weapon 45-cal. pistol, M-25 plotting board, 81MM sight
  • 1 x Ammo Cpl (Cpl. E-4). Official weapon 45-cal Pistol, M-25 plotting board, 81MM sight
  • 1 x Forward Observer (L/Cpl. E-3, Cpl.E-4  or Sgt.E-5). Official weapon M-14 rifle, map co-ordinates, ammo
  • 2 x Gunner (Lance Cpl E-3 or Cpl E-4). Official weapon 45-cal pistol, sight in mortar, Bi-Pods
  • 2 x Assistant Gunner (L/Cpl E-3 or Cpl. E-4). Official weapon 45-cal pistol, mortar tube
  • 10 x Mortarman (Pvt.E-1, PFC E-2, L/Cpl E-3). Official weapon M-14 rifle. (#'s1..outer base plate ring, #'s2..inner base plate, #'3,4 & 5...barber pole red and white striped aiming stakes and the red and green and white flashlights that attached to them for night firing, ammo - We ALL carried ammo on field ops).
  • 1 x Radio operator attached to the mortar  platoon. Official weapon, 45-cal. Pistol, PRC-25 & PRC-10 radios, batteries and accessories, sometimes ammo
  • 1 x Wireman ( sometimes ) attached to the mortar platoon. Official weapon ?? Communications wire spools and com line phones...ammo

Mike this is/was the ideal, perfect situational structure. Seldom in Nam did I ever have more than 06 mortarmen.10 is, as I said, what the book says.

DEPLOYMENT and ROTATION

Deployment was two fold:

Battalion was the hub and the sections were the spokes. We rotated (with the Company) as a platoon to and from Battalion HQ to the field positions. (This is why MIKE and INDIA swapped places and how I came to know Mike Pomakis and his Mortar team). We covered the incoming teams positions sort of like this: MIKE in, INDIA out, LIMA in, MIKE out, KILO in, LIMA out etc. This way each company mortar platoon rotated from into Battalion HQ out to every other companys position at one time or another.

Two 81mm mortar crew with their 81mm mortar
USMC 81mm Mortar

We were involved in a total movement as a unit on an operation. We moved both guns with the Company in large operations and we moved one gun with a smaller part of the Company in smaller operations ('sparrow hawks').

'Sparrow Hawks' were operations larger than daily routine patrols but were smaller than OPERATIONS involving the whole enchalada picking up and moving. They were short in duration (a few days at most) and were often hammer and anvil in nature, i.e.3 companies form a blocking force, set up position and wait. The fourth company, with much air and ground fire arty support, then sweeps through an area and pushes the VC toward the waiting group. I have also heard them called "swifts".

I have supported fire missions for more than one company at a time and also for the USMC. and the U.S. Army at the same time. This is common and one of the reasons for overlapping tactical areas of responsibility (taor's). We can cover our buddies and they, in turn, can cover us.

Battalion had two (2) sections or platoons, consisting of two (2) gun teams each. That's four (4) mortars/tubes. While there were always this amount of guns and men, mike, ya couldn't consider it static because when Battalion guns were relieved by Company guns the "out" rotating platoons took their 81mm with them into the field and the "in" rotating platoons brought their guns in to replace the outgoing ones.

We always stayed with our own company, i.e. MIKE CO. It is just that we rotated in from field positions and then rotated out to field positions. These could vary but we didn't switch companies. Let's say INDIA rotated from hill 10 to Battalion HQ. MIKE would rotate out to LIMA's position at say hill 35 and LIMA would rotate to INDIA's old position on hill 10. KILO would stay put. Next time around INDIA might rotate to KILO and KILO to Battalion HQ. MIKE AND LIMA would stay put, or might simply swap positions. I think the purpose of these rotations were two fold. Relief to a hard hit company and to keep us sharp by sending us "refreshed" units out to a "NEW" position where unknown danger lurked (LOL, as if it weren't all dangerous). I also think this confused the hell out of the enemy and demoralized them as they had no "fresh & new" replacements and to him/her, it seemed like a never ending stream of us were available to fight them in the field.

The 60MM's were assigned to the smaller outposts, i.e. MIKE held hill 52 but one squad operated out of hill 25 in-between MIKE and Battalion HQ. MIKE rotated these squads and I am not sure how the 60MM personel were rotated.

The Battalion HQ NEVER let more than one gun from each team be deployed before replacing it with an incoming teams gun that was in position to fire. This meant the incoming gun was seated - i.e. a shallow pit was lined with sandbags and the mortar fired several times to seat the base plate. They always had 4 guns at the ready. 1/2 the Company platoon rotated in with one gun, then the out going team was dispatched to the field, seated their gun, and then the incoming other 1/2 from a Company field position moved to Battalion HQ. and repeated what the first gun had done, then the other 1/2 of the outgoing platoon went out to the Company area and fixed the second gun into position. The primary mortar used in the daily patrols was the 60MM. It was lighter and easier to carry and run with.

Field companies had one (1) section/platoon consisting of two (2) gun teams and two (2) mortars/tubes

Squad is a term I have heard used State side for the two (2) gun teams that make up a mortar platoon but the more common term is gun team one (1) or gun team two (2).

AMMUNITION

Rounds carried - as many as possible! Usually 5-6 per man depending on type. Yes, the grunts sometimes also helped out.

HE Medium = larger round, farther distance, bigger bursting radius (approx. 35 meters). A 12-gauge shotgun type primer in the tail assembly ignited "powder" increments wrapped around the tail assembly above the fins. The amount of increments determined distance of travel. I cannot remember the exact distance but think 4200 meters for some reason was max? Exploded upon impact.

HE Light = smaller, less accurate round employing a cheese type plastic explosive charge that clipped on to the tail assembly. Less distance and smaller bursting radius (25/30 meters). Exploded on impact. 2800-meters approximate range? WE HATED these rounds. Lot of hang fires, duds and short rounds due to bad increments and it being "old" ammo. The VC would later find these rounds and make booby traps from them.

AIR BURST HE Mediums. Same as above HE Medium but these could be hand or tool set to explode above the deck before impact. Same dist & bursting radius as HE Medium.

81mm fire mission being conducted from a fire base
USMC 81mm fire mission

Illumination = same set up and charges arrangement as HE Medium and I think the distance was approx same distance. Hand/Tool set to explode in the air. I wish I could be more specific on the distances but my mind cannot seem to wrap around this question. It vexes me as I used to set 1000's of these rounds and also had to know the correct elevation and deflection ratio to increment charges to pass on to the men in the gun pits. This was essential to put the rounds out where the FO wanted them. An error of the slightest could be fatal to the guys in the field. I will explain this later.

PLOTTING BOARDS M-25 and M-10

The M-10 was primarily used by the 60MM. However 81MM did use these boards in field op "on the run" movements simply as they were convenient and less bulky. M-10 is about the size of a paper back book and an M-25 is about the size of an atlas. Both being slightly larger.

This is a toughie but I'll try to describe these boards in appearance. The boards were in the shape of a D with a + permanently marked on it and tic marks permanently marked on the top. The plus squared the board to zero and the tic marks represented deflection marks for the gun info needed to accurately fire the mortar. Now, picture a circular plastic disc, with grid squares permanently marked on it, snapped into the center of the D shaped board. Imagine it like a basic clock dial. The two gun positions were marked on the board as 1 & 2 and pointed true north. Here is where it may get tricky for you to understand. Using 12 on the clock-face = the zero point of the board. Perhaps 2 would be the actual "true north" position of the guns. The gun-sight was 'zeroed' and the mortar set to true north by using a compass. Then two aiming stakes were aligned on the front and on the back azimuth of the compass through the gun-sight; this set the gun to true north. The barber pole aiming stakes then acted as a reference to line up the gun on. We used a green/white (North) and a red/white (South) flashlight attached to these two front and rear poles to be able to align the guns at night. It was imperative to have a correctly aligned board and guns.

Also marked to "true north" on the board was the map coordinates. When a FO called in a fire mission, the gun positions on the board were brought to the 12 o'clock position, the coordinates being called in were plotted and this gave the elevation needed to calculate the powder charges needed to put the mortar round out where it was needed. Then the board was re centered to give the deflection (position the gun needed to be moved to the right or left). The sight was then set with this deflection and the gun moved until the sight lined up on the aiming stakes.

MORTAR COMPONENTS

  • Inner ring base plate with 'U'-shaped collar in the center into which the tube was inserted and then rotated into a locked position.
  • Outer base plate ring and clamps. Fitted over the inner ring and was locked into place.
  • Bi-pod and yolk assembly group. Tube inserted through yolk and then into base plate. Rotated into locked position in base plate then tightened and locked into position in yolk. Left leg of bipod had a tubular adjusting nut for gun cant and was used to level the deflection bubble. Also a right to left centering arm to make minor adjustments right/left. A center adjusting nut for elevation leveled the sights elevation bubble.
Full picture of the US M29 81mm mortar Close-up of sight mounted on US M29 81mm mortar
US M29 81mm Mortar Close up of sight mechanism
  • Tube. Fixed center fire type firing pin inside the tube for drop fire. Ball-joint type butt end inserted and then rotated into the inner base plate 'U'-collar and locked into place. (Note, the 60MM could be both drop fired or lever fired. The 81MM could not.)
  • Sight. One swivel type eye sight with elevation and cant bubbles to adjust elevation and right or left gun cant and deflection.

FIRE DIRECTION CENTRE

Perhaps this will be less confusing. On patrol, the Patrol Leader (usually an officer - but not always), radioman and mortar FO (sometimes also there were naval gun fire and artillery FO's along) were together in the column. When the shit hit, the FO would relay the map coordinates to the RTO to call in to the mortar position back at the Company position. The RTO used a PRC-25 to relay and it was received by a PRC-25 in the Mortar Fire Direction Control bunker at Company. The alarm was sounded: "FIRE MISSION GET ON THE GUNS".

Now, so you will understand the FDC, o1 = Gun 1, o2 = Gun 2, O=FDC;

o1------O------o2

Land lines ran to each gun pit from the FDC bunker. The gun dope was plotted inside this bunker and relayed to each gun and also to the Command Center. The position to be fired upon had to be cleared through channels. Company to Battalion, Battalion to Regiment, Regiment to Da Nang. Screwed up huh! Well, that's the way it went. BUT, once ya got permission, it was katie bar the door.

The VC would often go into Intelligence and declare their undying love for the US and hatred for the VC. A good guy pin was then inserted into their village map position back in Da Nang. If we got hit from that village and requested permission to fire it was denied. Didn't take anyone too long to figure out that calling a mission in on rice paddy would give the go ahead and then the FO would shift fire to the true target. Grunts can always figure a way around the brass's red tape.

A PRC-25 was the normal radio used. Look at Mike P's page and you'll see one with the antenna on his back. It is about the size of a pack. A PRC-10 is a hand held walkie-talkie sized radio used on 2-3 man 'snoop and poops' and out of the perimeter 3-man listening posts scattered around a position to listen for the VC sneaking up on ya.

I held the position officially as the Ammo Corporal, but in actuality was the Section Leader as we seldom had a Sergeant for this position. The breakdown inside the FDC is supposed to go like I am about to explain - but in reality I was the one in there doing all this. Fact not brag here, Mike.

Land line, headset (ear pieces like ear muffs) and a chest mic with talk/listen button. M-25 & M-10 Plotting boards, compass, gas lantern, flashlights, (white, red and green) colored marking pencils. These kept ya from plotting the wrong gun coordinates in the event of several different missions going on at one time, i.e. gun 1 is firing for 2-3 patrols getting hit and gun 2 is firing for one patrol getting hit from different angles. Gun 1 plots would read 1a1, 1b1, 1c1. If the gun had to readjust for any of these 3 it would then use the # designation for the change as 1a2, 1a3 etc. 1b2, 1c2, 1c3 this shows that a had 3 changes, b 2 changes and c 3 changes in coordinates. Similarly gun 2 would read 2a2, 2b2, 2b3 etc. showing one change for a coordinates and two for b coordinates.

The coordinates came in via the field FO to the field RTO that was right next to him. The Section Leader plotted the coordinates and used the board to get the guns what direction and elevation were needed. He passed this info orally to the Ammo Corporal. The Ammo Corporal relayed these positions and the powder charges the book gave for the necessary distance, to which ever gun(s) were to fire, via land line headset. The 1st Ammo Carrier got these via headset and relayed them to the A-gunner and gunner. The rest of the ammo carriers broke out the ammo and removed the safety pins. When the order to fire was given the gunner removed the sight, bent over and held onto the bi-pods and the A-gunner dropped the rounds passed to him by the ammo carriers. When the rounds requested were expended the gunner replaced and reset the sight to the aiming stakes - the percussion usually knocked the gun slightly off the coordinates. He then waited for new gun dope.

MORTAR POSITION

To answer your question about mortar positions, size of gun pits, etc. let me remind you of Mike Pomakis' site. There are some good pics there of mine and of several other Marines' that may help you out visually.

In general, a field position was laid out like a wheel. FDC was the hub, the guns at 3 and 9 o'clock, gun 1 and gun 2 sleeping bunkers at 2 and 11 o'clock. Each gun held a storage of ammo. Approximately 40 HE Medium, 10 HE Light, and 10 Illumination. The main ammo storage pit was usually located just beyond one of the gun bunker sleeping bunkers. Approximately 400 rounds of HE MEDIUM, 200 rounds HE LIGHT and 100 rounds of ILLUMINATION were stored there. Often however, it was less.  Now Mike, ya got to understand this was NOT always the arrangement as the terrain and defencability dictated the positioning of EVERYTHING, not just the mortar positions.

We had 3 perimeter wires. The outer most, or first line of defence, was usually a 10 ft. deep grid pattern of barbed wire lain down flush with the ground ending in a 3 strand fence row of barbed wire standing vertically and was joined at a 45* angle on the bottom of the parallel to the ground barbed wire to the vertical barbed wire. Kind of like a backward figure 4. (Hope this makes sense.) We called it the "cow fence". Approximately 10/15 feet was open and mined with claymores. The second row, or perimeter of defence, was essentially the same except that it had a row of spiraling concertina on the inside and backside of it. This was also mined with claymores and was in grenade range. About 6/10 feet beyond was the last line of defence. It was concertina and razor wire. 10 feet beyond was the trench line.

The side doors to the first row of grunt bunkers usually opened directly into the trenches. Machine gun positions were usually at the opposite ends of the position to maintain crossing fire and could be moved as necessary. The second row of grunt bunkers were approx. 20 ft. behind these, and then the mortar positions, then the Command Center. After that, we were dead meat!

SECURITY

Mortars provided their own security and were assigned to grunt trench or machine gun posts as help and were used on almost any working party necessary to the Company from filling sandbags, toting H2O, unloading choppers to pulling grunts rifle posts.

On a movement involving mortars they were usually in-between the first and second squad of the field platoon. Not always. We set up immediately if we were engaged, and used the direct fire method (which means the gunner looked at the target and guessed) and nightly if we weren't engaged, we set up hasty positions, when in the field. we could do this pdq. We carried a standard 4 magazines of M-14 ammo, 4 magazines of 45-cal ammo, depending on the assigned weapon. However, most all of us that carried 45's and had an M-14 stashed. We carried as much extra ammo beyond the standard as each man felt personally comfortable with and many of us sent home for, and carried, personal side arms. I have seen everything from Derringers (why I don't know) to 22-32-38-357 caliber revolvers. It was pretty stupid looking back on it, but scared men do stupid things I reckon. We did this also because, after we ran out of mortar ammo, we were after all just basic 03's with a job to do.

M-60's were carried by machine gun teams attached to the line outfits. They were a weapons section just like mortars were. M-79's, LAW's and 106's were the same.


A few things you may find of interest and that may also clear up some things about mortars and mortarmen.

In 66/67, when I was in Viet Nam, the Marines were, in general, overlapping units in what is the I Corp or northern area of South Viet Nam. The Army also occupied some of this area Mike. Their positions are something I am not all that familiar with except to say that they were on a much more permanent nature and basis. We were much more mobile, and often the entire Regiment, Battalion, and all Companies moved from place to place. In late '66 we had come from the northern area of Quang Tri on the DMZ to a more permanent area. It was about this time that the U.S. Armed Forces began to view the war in a different light, in my humble opinion. What we had been doing was simply NOT working. Like anything else, we had worked out the kinks so to speak and it was time to review and regroup the thinking of this always moving shit. In speaking with my Army friends they were utterly stupefied to learn of all of the men & supply problems the USMC had faced up until this time of "settling down" happened. Here is where you may have been having a problem in understanding what I am relating to you as "MY" experience Mike.

On an operation a mortar had to be set up and in action quickly
USMC 81mm mortar section in action

We were ill-supplied most of the time. Replacements, food, ammo, clothing and medical supplies were at a premium to us. So was everything else. We were a pretty ragged & rag tag bunch. Most of us had sewn our utilities (jungle fatigues) with comm wire and were without boots at times. Our flack jackets were given to the grunts. (No we were'nt just being generous, we didn't have to lug the dang things that way.)

Early in '67 the forces divided and the Marines took control of things north of Da Nang and the army south of Da Nang in general Mike. There were still overlapping posts and the southern area of Chu Lai was still occupied by the Marines simply because the Navy ran river boats up the river to the army's out posts that they had taken over from us in this transition.

It was at this time, about April '67, that we received the first M-16 rifles Mike. We also began to "beef" up the line companies to speed and then the attached weapons sections to almost a full compliment and strength. Prior to that the pickings were slim and to bare minimums to operate. I seldom had enough men - nor did the rifle platoons. :(

Some of the mortar equipment that I have forgotten to mention to you are:

  • Mortar tube bore swabs - one for each gun, a spare or two when available.
  • Cleaning rags.
  • Incendiery grenades to destroy the baseplate inner ring, tube, bi-pod, and sight in case of over-run.
  • Light oil for cleaning the guns and the weapons.
  • 1 K-Bar (Marine fighting knife and weapon of choice by Marines in close quarter fighting) per 45 cal. small arms carrier. (Mike, these knives were so coveted that the Corps issued an order to confiscate them if a person's job duties did not include carrying one.)
  • Everyone carried a side knife from home. Randall's being VERY popular.

Responsibilities I had to perform:

  • Morning, Noon and Night muster reports
  • Work and patrol detail assignments
  • ammo requisitions
  • supply requisitions
  • chow distribution - (12 different boxes of C-Rats to a case, 3 meals a day when able - means ya ate the same meal for breakie, lunch and supper for a month during a tour Just a quirky piece of useless info that I like to point out to people Mike..LOL)
  • Medical reports
  • R&R reports and tracking
  • Everyone's birthday
  • clothing requisition
  • Mail call
  • H&I plots to the Company
  • patrol coordination with grunt section leaders (so we didn't dump H&I's on them when they were on patrol - H&I's are randomly dropped rounds dropped onto known enemy trails just for grins and giggles and in hopes we might catch them by surprise.)
  • Ammo inventory
  • Damage reports
  • PM (preventative maintenance) daily, weekly and monthly
  • fire mission drills
  • equipment tests
  • training classes
  • promotion evaluations.
  • sanitation and health issues
  • Etc.Etc.


See Mike Pomakis' Account


My sincere thanks to Michael for all the help he provided in corresponding with me about this subject, it was both a pleasure and an honour.

Were you a mortar crew member or otherwise involved in the operation of mortars in Vietnam, either Army or USMC? If so I would like to hear from you in order to expand on this section and on mortars generally. Please contact me with your comments, all information is treated with the strictest confidence. Mike R.


 

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