The fixed Coaxial machinegun on the tank turret

How were these effective and what was its main purpose?

I looked at the internal design schemes of these guns and they appear as merely a fixed hole right next to the main cannon. While I understand how the forward machineguns (fired by the radio operator) is useful due to ball mount, the fixed MG confuses me. It has less shooting flexibility than the main cannon and the entire turret would have to line up and carefully rotate in order to track targets.

What I'm saying is that it seems more like a marginally useful bullet hose. It probably can't do much except pelt a certain area ineffectually before the HE is fired.


*The Hole*

 

Here is the sum of what I've read, though I've no personal experience in military armoured corps.

When the sights are knocked out or poor ones are fitted the coaxial MG is used to sight the main weapon. It is also useful for infantry defence of course, as the field of fire is roughly the same as the main gun, where a hull mounted weapon even on a ball mount is far more restrictive. If you were intending to lay down dedicated machine gun fire however, a pintle mounted weapon on the roof would do best.
Allied tanks sometimes have a light MG on a pintle mount for this purpose in addition to the pintle mounted heavy-MG for AA defence.
German MG are a bonus because they're dual purpose due to rate of fire, particularly the MG42 (MG34 were preferred for integral weapons however due to build quality).

 

Ironically, this has happened to Joe and myself when driving around in tanks in Red Orchestra: Darkest Hour. The main-gun sight got knocked out, so he couldn't see where he was firing. I jumped into the Radio Operators position to use the MG (better view then as a driver while buttoned up) and watched where the tracers of the main-gun-MG went. After a bit of trial and error, we knocked out the tank that knocked out our sights

The fixed MG also allows the gunner to target infantry to either side or the rear of the tank based on where the turret is facing - angles the Radio Operators MG can not cover. Plus, it provides an extra MG to suppress infantry.

 

Who said FPS couldn't be educational? ( Never look behind a shower curtain in Left4Dead either)

 

Well, RO does pride itself on its Realism! I really hate it when my Tank gets tracked and can only turn in on circle rotating around that tracked-track. Its sorta like an instant-bunker that can always present its forward facing armor to a target.

The gunner can also use the MG when seeking targets - many a time have I mowed down infantry with the MG while seeking enemy tanks.

 

Very interesting. I never knew that this MG was used to help site the main cannon.

 

Yes, firing the coaxial mounted machinegun to spot for the main gun would be much more economical that shooting spotter rounds downrange before firing for effect. Also, your opponent might be able to send one back before you could re-load, which would be a very bad thing....

 

Actually this is untrue. Rifle Caliber MG rounds have different ballistics than tank shells. In fact tracers have different ballistics than regular bullets so they are not even good indicators for regular bullets beyond a few hundred meters. Beyond 200-300 meters the tank shells are going to have a wildly different course than tracer rounds, and that differs between the velocity of the main guns.

 

If that is the case, was the MG used mainly as a superficial "bullet hose" for token suppression?

 

considering the realitively rapid turret rotational speed of the M4, I would think that its "suppression" of advancing infantry from either side or rear might be more than "token". And it would be a much more protected position from which to us a machine gun than the exposed .50 mounted on the top of the turret. Just a guess, but with the different ballistics of the two rounds (main gun, machine gun), I too would wonder at the "fire for effect" usage.

Just a guess on my part, but having a machine gun which can fire in directions besides forward of the hull must have been a consideration here. This cut-away drawing shows how the co-axial gun was mounted, and with the rapid turret speed of the M4s I suspect it was more effective than one might presume!

See:

http://www.wwiivehicles.com/usa/tanks-medium/m4a3.asp

It doens't really say who fires the MG, the loader or the gunner in the thing, but it could be a very effective "infantry suppression" device.

 

I'm guessing that to be the case as well. The forward MG could cover ground targets and the turret MG could cover elevated positions. I'm sure that the forward MG saw far more usage, though.

I also would assume that only one (the main gun and the MG) could be fired at one time.

I'm trying to imagine how clumsy it would be to track moving targets. I'm guessing that one man inside the M4 moves the turret and other man fires the machinegun.

 

I don't understand the question.

A machine gun that can be pointed at appropriate targets instead of firing the main gun & potentially wasting it's limited supply of ammunition - Exceptionally useful against softer targets, not much less flexible than a tripod-mounted HMG, and operated from within the safety of full armour.

Why not have one?

~A

 

I'm trying to visualize aiming and shooting the MG through the turret. Because there is no flexible mount like the forward MG, the gun cannot move up and down on its axis. It can only move from side to side.

 

The gunner for the main gun did this operation as well, also the turret rotation was controlled by the gunner with a "twist grip" affair (from photos I’ve seen), and it was 24° per second in rotation. Also the co-axial .30 also had a manual up and down ability of +25° up, and -12° down, so it wasn’t just a "bullet pump" rotating and shooting at one elevation.

The gunner, sitting slightly ahead and lower than the tank commander on the right of the turret controlled both the 360° rotation of the turret (in hydraulic function), and the firing of both the main gun and the .30 caliber MG. I don’t know the exact amount of ammo he had for the .30 in his control, but there were about 4,500 rounds of .30 carried for the two MGs in the M4. I don’t remember ever seeing how this was divided up between the two.

He did this through his sighting periscope for both weapons. In the case of the .30 I would imagine a good gunner could be counted on to have "figured out" where the MG shot in relation to the sights for the maingun.

 

Tank combat is typically close range, ie. 1-300 metres for penetration sake (German late war tanks are an exception and often dominated the battlefield because of it).

Considering MG fire from a vehicle is hardly precision sniper shots the spread of fire is useful for sighting the main weapon. Some tanks in major use weren't fitted with modern sights and according to publication (I can cite sources) the coaxial MG is used for sighting.

In any case a shell can land a few metres from a tracer round and still hit the same vehicle or bunker. The main gun ain't shootin at swallows, a ten metre CEP will do nicely.

At range where using the main gun as artillery you can still use the coaxial MG for ranging. Just calculate elevation to tracer hits and then recalculate for HE or AP rounds and boom.