"Use of machine guns for range estimation in WWII" Topic

I'm looking for examples of the use of coaxial machine guns to perform range estimation for the main gun in WWII. I'm familiar with it in post-WWII.

The only account I know of is the German Panther, Tigers, and Mark IV gun sight could fire a burst from the coax gun and then adjust the gunsight for the range the rounds impacted but the range was limited by tracer burnout.

The reason I'm interested in that it was normally SOP to fire your coax mg at an anti-tank gun because it was quicker and gave a better chance of suppression. It makes sense to me that if the coax gun burst is on target out to about one second time of flight the main gun should be fairly close, depending of course on how well the ballistics match. If so you should be able to follow-up almost immediately firing your main gun if you already had a round chambered of course.

Any historical accounts or his training appreciated.

Wolfhag

It makes sense to me that if the coax gun burst is on target out to about one second time of flight the main gun should be fairly close, depending of course on how well the ballistics match.

That small bit at the end, how close the ballistics match, will be one of the "gotcha's".

Let's take the example of an M4 Sherman tank.

Muzzle velocity of the .30cal M1919: 2,800fps
Muzzle velocity of the 75mm M3: 2,030fps

So at about one second of flight time, the .30cal will be just a bit less than 2,800 feet away. But the 75mm gun's M61 round will take almost 1.5 sec to reach that same distance, and so will drop about twice as far from the line-of-site. You will miss, by a pretty wide margin.

The issue will be less for some (M4 Sherman with 76mm) and more for others (Pz IV with short 75mm).

The keys are first how closely the guns are matched in muzzle velocity (the only point I have considered), but then also how well the ballistic efficiency of the projectiles match (which will vary depending on the type of ammunition being fired). In MGs the tracer rounds did not match the standard ball rounds in ballistic efficiency, leading the US Navy and Airforce to move away from tracers to API rounds as the tracers were misleading pilots to mis-correct their aim.

I could see it working at very close ranges (say 1,500 ft or less), but at those ranges I'm not sure you need to do much ranging. An HE round for effect might be the better "ranging shot". If you are short by a few feet, no big deal.

-Mark
(aka: Mk 1)

Most of the tanks of the time had stadia reticles.

Tracer burn out occurs around 700m for the MG ammo. So, looking at the reticle, a gunner just has to set up and select a target at say 600m and fire bursts at the target and make adjustments until the rounds land in the vicinity of the target. Then you reference where on the reticle that is. Example: At 600m the machine gun hits the target at the 16 line on the reticle. So, now the gunner knows the target is at 600m and he can then relay the gun site to that range for the main gun ammo.

This is a simple example and in no way represents how the practice may or may not have been done in different armies.

Good topic. Thanks.

Major Mike,
Thanks, but isn't the "16" on the sight 1600 yds? The manuals I've seen for the M1919 were 900m for tracer burnout.

The German TFZ series gun sights can do ranging as there is a different selection for the mg and main gun. However, I'd think it would be better used to help set up a Range Card than ranging.

Wolfhag

Some people are probably thinking why this is such a big deal. Well, I'm playing a game system where real seconds count in an engagement, and the amount of time to execute an order like shooting, will determine your fate. With each unit operating within its own OODA Decision Loop, the fastest units seize the initiative to shoot first with split-second results. Seconds count.

When a tank platoon engages an anti-tank defense it's the seconds that will count and a medium anti-tank gun that is not suppressed can get off 7-10 rounds per minute and they normally open fire in an ambush ensuring hits and penetrations (flank shots). This is much different from a game where you get 1-2 activations in a 10-30+ second turn.

The tankers actually have a dilemma; detecting a concealed anti-tank gun's muzzle flash that is 200-600m+ away a dug in and concealed gun will only be showing about 1.5 feet of vertical target to hit which is difficult enough but add to it that you are firing at where you saw the flash because you may not be able to exactly aim at that small of a target. So the commander can choose to fire his main gun but what if he has an AP round loaded? What are his options? If his AP round misses it most likely will not suppress the crew. A gunner that fires his coaxial mg first instead of his main gun has a chance of damaging and suppressing the target forcing all but the gunner and loader to seek cover. If a coax gun tracer hits the gun shield it will most likely ricochet potentially identifying the target while it is still concealed.

I agree with Mark 1 about tracers but it appears they were used by bow gunners as evidenced this British test with Cromwells:
link

and the Sherman bow gunner didn't have sight so he needed to use tracers observing through his periscope. I've also read about tanks marking targets for others using tracers.

I could not find many examples of identifying or ranging a target with mg's but here is one:

The Sherman bow gunner's position required him to be seated at the right front of the hull where his station was primarily dominated by the tail end of his bow-mounted 7.62mm anti-infantry machine gun in a limited-traverse mounting. Like the driver, the bow-gunner was also given the use of a fixed periscope after the dropping of the direct vision slots mentioned earlier. The bow gunner's position proved useful in engaging and suppressing known enemy positions (as related to infantry) – an important component in the Sherman's arsenal when combating anti-tank gun crews. To prove the position more important, the bow gunner could also "mark" targets or help "range" the main gun onto a target (or suspected enemy location) via his machine gun tracer rounds which could be utilized to orient the gunner's cannon with.

Personally I don't think he could range the target other than by tracer burnout but he could help designate it with tracers if no one else saw it.

Based on the tracer and main gun rounds not being ballistically matched I doubt if any real effective ranging could be done as in post-WWII with dedicated ranging mg's as Mike and Mark pointed out. In addition, most guns went into battle with a "battle sight" setting with the gun elevation being set for the range they'll most likely encounter an enemy, usually out to about 1 second time of flight. So rather than taking a lot of time to the commander and gunner to get a good range estimation, the gunner would give it a quick look, and if under 1-second ToF (700m to 900m) he'd aim at the bottom of the target. If over 1-second ToF he'd aim at the top of the target. While less accurate, it got the shot off 3-6 seconds sooner. That's the speed versus accuracy dilemma crews faced.

So on a real battlefield, if a gunner engaged an anti-tank gun with his coax mg what advantage, if any, would he have if he follows up with his main gun? Would the advantage be in accuracy or a quicker main gun shot? After reading the Fm17-12 tank manual it didn't indicate ranging machine guns.

Wolfhag

So, here is FM 17-12 AAFM from 1943, I direct your attention to pages 5-6, 28-33 and most importantly paragraph 48 on page 34. PDF link

Major Mike, thanks an interesting link.

The only tanks that I am aware of that used the co-axial mg as a ranging device were the post war British Centurions and Chieftains

Mark 1 is quite right, the ballistics match is essential for ranging in these circs …

in the Chieftain that I (long ago) crewed we had a 50 cal as a reversionary mode of ranging, if the laser range finder packed up. we also had a 7.62mm coax which was not matched and therefore of little use in that role.

these ranging 50 cals were a big thing with the Israeli armoured corps, I recall, mounted over the 105mm main armament, firing single rounds of tracer for ranging purposes,
EC

There was a German circular that recommended alternating AP and HE when firing at anti-tank guns. I don't know what the date and for what guns this was for. But, for most German tank cannons the AP and HE had completely different ballistics and this would be impractical.

I can do a comparison of the trajectory of the 75mm M3 vs a .30 cal M2 ball round shot at the same angle. It looks like a close approximation out to 300 yards then also at 900 to 1000 yards.

After doing some additional searching here is what I found:

Use of the coax for ranging was not recommended because it gives away your position, of course the main gun does too. But it does give targets a few seconds to react.

It appears the ballistics of the mg don't need to exactly match the main gun. The Sherman gunner used the aiming reticle differently for different round types. The German TZF and Soviet gunsights have a separate reticle for the main gun and coax mg which I'd expect would make it fairly easy to do. You could also use the coax to range in on specific locations to make a Range Card.

The Merkava .50cal is mounted coaxially but does not seem to function as a ranging gun. They didn't use them on the Golan front, only in areas expecting urban combat. Mounted coaxially allows them to be fired without exposing a crew member to snipers. It can take out targets in buildings better than the .30cal coax and less chance of civilian causalities from the main gun. The Osprey Merkava states it was used against helicopters without exposing the crew and counter-guerrilla operations. There was no mention of a ranging machine gun but I'd expect an experienced gunner could use it that way but why bother when you can use a laser rangefinder that won't give away your position.

Would an experienced gunner be able to use a coax mg as a way to decrease the range estimation error even if the rounds do not ballistically match the main gun? Since the mg rounds would only be good out to about 1000m would it even be worthwhile to use it that way?

The only advantage I see is if you engage an anti-tank gun with your coax first it would be quicker than firing a main gun round and should get some suppressive effect on the crew. If the coax is on target it should help in increasing the accuracy of the main gun which could fire seconds after a coax burst. That's what I'm thinking but I was never a tanker.

Wolfhag

Very interesting ! When I was on Active Duty well after
WWII, we didn't have anything that used a ranging MG. Much better systems around, obviously in the '80s …

Legion 4,
The 106 recoiless rifle has a .50cal spotting rifle firing special rounds and the SMAW has a 9mm spotting round. But then you never had them when you were in.

Wolfhag

Yes, I remember hearing that now … Yes no 106s when I was in. And the Army did not have SMAWs either then.

We had the 106 at Battalion level mounted on Mechanical Mules. They were replaced by TOW's around 1980 I think.

It would be interesting to see how they would perform. With a low silhouette they'd be hard to spot. After the spotting round hit the target the crew shoots and then immediately moves out so even though the back blast gives them away you can't return fire very well.

Wolfhag

I spoke to a good friend of mine that was a Marine M48A3 tank gunner in the early 1970's. He said that it would be quite easy to follow up a coax burst that was on target with an accurate main gun round just as long as you could observe the tracers. The M48 has an integral rangefinder making it easy to get on target and not needing a ranging coax. He said it was common to "bounce" an HE round with a delay fuse just short of the target off the ground and have it go off as an air burst over the target.

Wolfhag

Yes, we had some M274 Mules when I got to the 101 in '80. But used only to transport ammo, cargo, etc., and even troops sometimes.

Good intel on the M48A3 …

Bouncing an HE round is nothing new. The US and Germany did it. The Sherman HE round was the most effective doing it because of the HE charge and delay fuse that gives an air burst 8-10 feet above the target after traveling about 25 yards after bouncing. Of course, you can't bounce rounds off soft ground. That's going to be deadly against an anti-tank gun crews. I haven't seen any rules that include it.

Using the Sherman 75 commander turret override and vane sight (faster detection and engagement) with the gun bore-sighted to the expected range of a threat the Sherman could get off an HE/WP round and a coax burst in 5-7 seconds. Since the gunner has a panoramic roof periscope he'll pick up the target quickly after the commander has the gun pointed at it to accurately engage follow-up shots every 5-6 seconds.

That's under mostly ideal conditions at about 500 yards maximum effective range for a first-round hit, maybe less. That's what I'm modeling in the game. The Sherman has some really cool features and advantages that most games seem to leave out. The more I know about it the more I like it.

Wolfhag

A good tactic if the crew survived long enough to master it. Even M4s would aim for the Mk.Vs and VIs mantel. Bouncing off the mantel, the round would fall on top of the driver and bow gunners locations. The armor on top was much thinner than the front of the turret. Again it took experienced crews to do that with any regularity.

And one of the reasons the Mk V Panther had its mantel modified in later models.

I read an account of US Tank Destroyers (not M36 Jacksons) ambushed Panthers in a fog and were able to aim at the BMG location and get a penetration. Being in the fog they were able to get close enough.

Hitting the mantlet bottom, BMG or any weak spot could happen by chance too. That's why when rolling for the hit location I use a 5% chance (1 on a D20) of a "Critical Hit" on a weak spot, turret ring, etc. No tank is completely safe at any range.

Wolfhag

And one of the reasons the Mk V Panther had its mantel modified in later models.

Yes, I built models in my youth of both types of Pz.Vs. One with the modified mantel …

Being in the fog they were able to get close enough.

Again weather conditions can be critical …

Yes, IIRC, it is called a mantlet … not mantel …