"Machine guns Firing on Fixed lines" Topic

I did some analysis on this as it seemed odd to me that more recent rules have stepped away from this form of fire so have moved a long way from reality, even Phil Barker got this bit of Machine gun Tactics accounted for.

Firing a Machine gun on Fixed line

I have long been interested in firing a machine gun on a fixed line (an FPL line.)and why this is better than say spraying an area as a last means of defence. Here is an analysis that I undertook that may be of interest for folks with an interest in such subjects.

Fixed line basline Assumptions

Machine gun Rate of fire 100 RPM = 1.67 Rounds per second
Based on continious fire used in US MMG WW2 tactics, well below maximum Rate of fire.

Maximum rate of fire 650 RPM Lowest typical rate quoted for M240.
Muzzel velocity a 2700 ft/sec a bit lower than spec (M240) for slowing down.

Man walking at 3mph= 4.4 ft sec.
Target width 1 ft (man seen sideways.)
Length of target (prallel to bullet stream) 2ft

Graving fire assumed so bullet never more than 2 ft above ground for 600 yds.

Also assumed if a bullet passes through the target it causes incapacitation and that the target cannot avoid being hit by changing pose or interveneing ground.

The analysis assumes a perfect fixed, no dispersion, line a bit of a simplification.

Analysis

Time for man to pass is through the line of bullets 1' / 4.4'= 0.22 sec
Time in the path = 2'/2700=0.00074 sec. Not much diferent to 0 so 2D target used as a a conservative assumption.

So odds of hitting a man is 0.22/1.67=0.133 or 13.7%.
At 650 RPM the frequency is 650/60=10.8 rounds a second or 1/10.8=0.0925 sec between bullets.
Hence 0.22/0.0925= 2.378 hits on average. Massive overkill.

So optimum kill rate is 0.22 bulets per second. 272 RPM.

Traversing an area with Grasing Fire as a comparison

Basline Assumptions

Assume its an area 150 ft long by one man wide. This covers a small angle 4.7 degrees which is small so traverses can be considered parallell to man track
Time to walk over this area is 150'/4.4'=34 seconds.
Assume a traverse each way of 10 seconds. This is more than 3 passes of the area in the time the target traverses the area.
Assume 272 RPM so 4.55 bullet every second.
Threfore in the time to traverse the beaten zone there will be 4.55*10= 45.5 bullets fired.
So the horizontal bullet spacing is 150/45.5=3.926 ft
Now the man is 1 ft wide so odds of hitting once on a pass is :-

Change of being in the space as the bullets pass 1/3.926 = 25.47%
Odds of being hit if in the space 100%
So each pass proability of not being hit=0.7453^3*0.7453*0.4 (3.4 passes of the MG) = 51.4%

Conclusion

A fixed line of MG fire is 100% effective at 272 RPM in this calculation but only 48.6% effective in traverse mode.

Clearly in reality 100 RPM has a very high lethality as part of a 3 man MMG platoon and the dropping out of 1 of the weapons as it moves/reloads/changes barrels can easily be compensated for by the other weapons increasing fire rate by a small amount.

While it is possible to argue the exactitude of the numbers, please feel free to critique the assumtons as well.

The analysis does show clearly why a Final Protective fire line, surveyed to ensure maximum effcet of grasing fire is the ultimate killer. Speeding up the traverse to say 5 seconds actually increases survival as does widening the traverse angle.

Of course it does give the position of the MG'away as its fireing continiously so unless in an Artillery proof bunker it does not want to be revealed too early as it soon becomes a sitting duck. However it does have the advantage it does not need tracer rounds as it is a pre surveyed line of fire so fall of shot observartion is uneccessary.

Yes, we were taught about using FPL in the Defense. And if that was the tactic you wait until the enemy is in the FPL. To get max effective. As you don't want to have your MGs drawing anymore fire than you have to.

As with all heavy weapons, there is a good chance that they will draw direct and indirect return fire. Or possibly even prep fires if the attacker does a good analysis of likely enemy position locations.

Do you know what a T&E mechanism is for an MG ? Or a Range card ?

People are not going to walk into machine gun fire, so I think you can throw out your 34 second calculation.

In FPL you are using grazing fire across your own front, and the terrain needs to be flat or have a uniform slope. In your example, a target 1 person deep by 150 persons wide would be an ideal target for traversing fire.

There are many ways to fire a machine gun. "Spay and pray" implies a lack of control and intentionality.

That is true, generally the first burst will inflict a number of casualties. Before the rest go to ground, take cover, etc. The MG(s) FPL along with other weapons in the unit, organic and indirect support, opening up. Is meant to stop or slow the enemy attack(s). Force them to withdraw, or move into minefield, etc., etc. Or attack from another avenue of approach, where the defender may have to "Lift & Shift" and of course both continue to call in supporting fires.

The "spray and pray" ia a clasic Hollywood action. The intent was to convice myself of the logig of an FPL.. Most certaily its not the only use of MG fire. It can be used as an area fire weapon. An ex serving soldire said it was considered again in the cold war period. It was most certainly use in WW1 and 2.

On ex servicemen noted for an MG it was 3 for range and 5 for effect. But of course whis was not for an FPL. However any normal case of even a platoon deploying in defence they will get out the tripods for at least some weapons and set up FPL(s).

this video is great . YouTube link

the use of indirect fire / area fire by HMG was used in WW1 and WW2 . You rarely see it in game rules .

Included here (page 18) is a 7.62mm "D" ball DP machinegun firing table. Which gives the trajectory height at 600m as 1.1 meters.

PDF link

The term doesn't just apply to defensive flanking fire. Oddly, it is also ( sometimes) used for pretty much any mg area fire whose lines may not be particularly fixed.

link

An indirect fire method could be used from reverse slopes.

Perpendicular fire could also be used to mark the edges of an advance corridor whilst discouraging any potential enemy flanking move.

Machine Guns & Machine Gun Gunnery USMC manuals
1996 PDF link
2016 the newer one link
just look at Chapter 6

Both the M60 and M16 used bursts rather than constant fire.
My gun jeeps scout M113 were assigned both a .50 caliber and a M60.
We did a sanctioned field test during the DRS study to see how many rounds of constant fire it took on a used barrel before it melted. It was strange to see the barrel droop before the rounds exited the side.
The 30 caliber coax could not be feed enough rounds in the fixed main gun position for it to melt.
The development of the Haye bunker utilized the fixed inter-locking firing position to create a kill zone. The bunker had a solid reinforced font, no firing slits. The MG firing slits were at 45 degree angles so that the rounds would land in front of the other bunker. This created a double gun kill zone set between the bunker which is where charges tended to gather. Support troops in the bunker were supposed to concentrate fire on the bunkers firing slit area. Coverage was pretty much complete.

Walking sailor that link is a real winner. It rationalises the 600m we had read before and gives the sort of infomation I have not seen before.

We (Maneouvre Group) have been using. Frome the table on page 6-13 sighted range, 500m max deadspace 15" max coverage 560m. sited range 600m deadspace 31" Max coverage 680m.

Mobious I guess its all about variation bullet to bullet as to why the height is a bit higher in your table.

Mow interestingly at 600m 3 degrees (the safe distance from friedlies is 30m, (this is 30mm at our scale). Much less at closer ranges.

On that basis our assumption of just a line is proably good enough with an assumption if the line crosses a base it hits, our assumption looks acceptable and its not worth the complication to have a more complex rule.

Manual tables made for Marines I guess as ranges are in meters and velocity in feet per second.

Walking sailor that link is a real winner. It rationalises the 600m we had read before and gives the sort of infomation I have not seen before.

We (Maneouvre Group) have been using. Frome the table on page 6-13 sighted range, 500m max deadspace 15" max coverage 560m. sited range 600m deadspace 31" Max coverage 680m.

Mobious I guess its all about variation bullet to bullet as to why the height is a bit higher in your table.

Mow interestingly at 600m 3 degrees (the safe distance from friedlies is 30m, (this is 30mm at our scale). Much less at closer ranges.

Also I now have some sensible data to cover plungeing fire Max width looks to be between 100 and 50 mils. Looks like a standard value of 75m width looks OK and 150m long.
YAHOO issue 2 will have a set og MG'rules I can count as credible, the MG has long been a bain to get right, it was obvious that many rules got it wrong but getting it even basicaly right has proved difficult.

I suppose I ought to start an official set of references for Maneouvre Group but nobody ever asks, which is a shame in many respects.

On that basis our assumption of just a line is proably good enough with an assumption if the line crosses a base it hits, our assumption looks acceptable and its not worth the complication to have a more complex rule.

It's not just the MG's in FPF. Each rifleman has a designated direction to diagonally FPF generally with a stake in the ground that he puts the rifle against and fires. This works even at night. Then your 60mm mortars may be dropping rounds within 25m of the dug in defenders. It's a team effort. The signal was generally a star shell of a particular color fired by the Company Commander.

If there was barbed wire the MG's and Claymores would normally be set up to fire along the wire where the enemy would be held up or attempt to pass. Dead ground and depressions would be pre-registered for mortars. Heavy mortars would target suspected staging areas further out and put up flares if needed.

In WWII the attackers generally probed the defenders at night to get the MG's to open fire so they could target them before the main attack. At night the Marines brought up the water cooled .30cal Brownings because of their sustained fire capability and not needing to change barrels like with an M-1919.

One of the best accounts of a nighttime defense and FPF is the account of the Marines (6th Marines?) on the 2nd night at Tarawa.

Wolfhag

We (Maneouvre Group) have been using. Frome the table on page 6-13 sighted range, 500m max deadspace 15" max coverage 560m. sited range 600m deadspace 31" Max coverage 680m.
Mobious I guess its all about variation bullet to bullet as to why the height is a bit higher in your table.

That table shows that the maximum ordinate at 600m is 1.2m. I take this to mean the maximum height.
By table 3-53 the M80 ball has a mean radial dispersion of 0.3 m. Or in the German 50% system of 0.6m.

Manual tables made for Marines I guess as ranges are in meters and velocity in feet per second.

Marines (and most of the rest of the US military) really only measure ranges in meters. Firearm velocities and small-arm bullet weights are in feet per second and grains (7000 grains per pound). Even vehicle speeds are usually given in miles per hour, since that's what people are used to from the civilian life.

OK so nobody spotted my deliberate mistake ;-). In the fixed line Calcs I used bullets per second not seconds per bullet. This means that the hit rate at 100RPM for the fixed line is 33.4% not 13.7% as in the original. Shows never do calcs woth a headache!

Now it makes even more sence why the MG platoons used around 100RPM with a couple of guns that is VERY leathal fire.

It also highlighs even more how much less effective spray and pray is.

Wolfhag, the current(ish) manuals also use the underslung gernade launchers for indirect fire, using a stick to point direction and a line on the Sling where you put your foot to set the elevation. It is generally a problem in that we do not put in such terrain on the board.

We do allow troops to "find" masking terrain i.e terrain that is sufficent to hide behind prone, such that you cannot be shot at by direct fire weapons.

OK, so who in skirmish gaming actually puts in dead ground. We tend not to put small elevations in as it make for a complex layout at company an above games but would seem to make more sence for folk who use a maximum of a platoon.

I suck at math … But I do know something about Infantry ops and weapons …

So its interesting we are all talking about the facts but somehow the translation into a wargame bit of the discussion seems to be missing. Do folks just not care about geting their games vaugely plausible.

Oh and before anybody pulls the daft wargames satements like not involved in these issues at higher levels, I suggest they watch Dwight Shrutes excellent link (thanks for that) the Battalion Commander is discussing the MG platoons deployment so he is involved at much lower levels.

It's not daft to assume wargames rules focus on the command decisions at the level of command they depict.

Dwight's link is about HMGs – they're a battalion asset, in the heavy weapons company.

They're not part of a rifle company, they (and the mortars in there too) are his toys, to use to bolster his rifle companies.

The Battalion CO should be deciding where the rifle companies deploy, and where he deploys the support assets from HIS heavy weapons company.

That is not a lower level – its his job to do it and no-one elses.

The level you have tripod MGs is very dependent on timeline.

The modern Stryker Platoon (and US Army Infantry Platoon) has two M240s in Weapons Squad, and those are usually mounted on tripods in the defense. M240s are heavy pigs to carry for bipod work.

Yes, we normally never dismounted our .50s from the tracks unless in a Deliberate Defense. And our M60s were very rarely tripod mounted … again unless possibly in the Defense.

Do folks just not care about geting their games vaugely plausible.

I totally like and want a more realistic set of gaming rules. As not only have I pretty much played wargames all my life. Including 1 to 1 scale. In a variety of environments & terrain. But sometimes I have to decide what detail is macro level vs. micro level. And how much the X-Factors play into it as well.

Do we add rules that state if an MG Tm does not set up the weapon on a Tripod w/T&E and Range Card then their rolls to hit are effected ?

Or if the MG Gunner didn't get mail or didn't like the C-Rat he got. His moral is effected and the MG's rolls to hit are diminished ?

Certain rules in replicate some level of reality and some don't. But we pretty much all know can't replicate all the factors or paradigms of the RW battlefield. On a gaming table. We can only get so close. And in many cases what some accept in gaming rules is not what others think are "good", acceptable, etc. E.g. IGOUGO vs. Unit Activation. I don't like games that are "straight" IGOUGO. So I don't/won't play'm …

Legion 4

It is always stared that the machine gun is the most powerful ant infantry wepon on the battlefield. Therefore its implementation is key. So yes in defence it needs to have an FPL assinged to it if the commander wants one, if its on a Tripod and has sufficent ammunition dumped with it. It will be difficult to move far from its initial position as its Heavy in that role and needs a lot of amunition.

Better to scrub off rifle rules as they are less powerful if there are too many rules overall. By its very nature an FPL will have diffrent die rolls to it being in other roles.

Morale, I have read lots of books, what I read it that supprisingly in most combats the troops do what they are told to untill the casualties are very large, even when very cold and hungary. I suspect it is the usual daft approach in some wargams tois massively over represented. If you believed some rules Victoria Crosses would be handed out in the hundreds not by the handful in the entire war as in thre real world.

Yes … I know all that … MGs, GLs, etc., will have different stats … than e.g. the standard issue Infantryman's rifle. And the if the rifle is semi-auto or bolt action will probably have different stats as well.

But again are the rules based on Fire Tm/Squad level or Plt or Co. level, etc. ?

E.g. just look at the counter of the old Panzerblitz game. The game is a bit dated now. But the example is still valid.

It is always stared that the machine gun is the most powerful ant infantry wepon on the battlefield. Therefore its implementation is key.

Again, I know that. I graduated from both the US ARMY Infantry Basic and Advanced Courses. Plus other extensive tactical training, etc.

As a Mech Co Cdr, each of my Squads had 1 M60 MG, 2 M249 SAWs and an M2 .50 cal on the track. So yes, I do have a "working" knowledge of employing MGs effectively. As well as GLs, Light, Med and Hvy AT weapons, plus mortars and even FA, CAS, etc.

Sadly as a PL in the 101 before that, the Light Inf Squad had only 1 M60/squad, and no SAWs or .50 cal. Fortunately the Squad did have 2 M203 GLs.

So if the game level is at Fire Tm, Squad, or Co., the stats at each of those organizational levels would be different. And be reflected in the counter or what other "devise(s)" is used to represent that. E.g. Minis …

By its very nature an FPL will have diffrent die rolls to it being in other roles.

Yes, at Fire Tm level the rules we used simply add +1 to hit if the unit does not move. And the Hvy Weapon(s) of that Fire Tm has it's own stats. Along with the stat for the basic Riflemen's weapons goes into one stat. I.e. One stat for the Hvy Wpn and one for the rest of the Fire Tm's rifles.

That takes in a number of factors for the troops. No matter what weapons they each have will be more accurate and effective because they are just shooting and not moving. Plus generally all Infantrymen when not moving on the battlefield will take cover, go prone or kneel down.

And yes, again I started playing in war games in the 60s. So I've used many rules sets. With some obviously better than others.

It is always a balance among complexity vs. playability vs. realism. E.g. AH's Squad Leader series of games is really probably one of the best for "melding" all three of those.

Morale, I have read lots of books, what I read it that supprisingly in most combats the troops do what they are told to untill the casualties are very large, even when very cold and hungary.

Yes, morale is always an X-factor, in many situations. But in reality generally "better" units, e.g. Rangers, Commandos, Spec Ops, Airborne/Paras, Marines, etc., will have "better" overall morale, etc. And as we see most games can and do reflect that.

Of course one should play with whatever set of rules they like.

The link below is the best read on the employment of machine guns, both in WWII and in relatively modern times.

PDF link

Interesting read, thanks.