Multiple Weapons for Armoured Vehicles

[rickshaw]

The thing is that these 20mm guns on tanks instead of MGs have tended to end up being replaced by MGs!  The reason is of course that the role of the secondary armament is not destruction of materiale but suppression and killing of infantry, something that a MG does just as well and much more cheaply.

[Weaver]

On the other hand though, 20mm weapons keep being proposed for a return. The AMX-30 had one and it's successors still carry a 12.7mm co-ax instead of the customary 7.62mm. MBT70 had one, and the various Croatian modifications to the T-72 have one or two depending on the version. One argument is that with increasing main gun calibre, the number of stowed rounds has gone down to the point where having a co-ax that can take out a light AFV without wasting a main gun round is a valuable asset.

I actually have no objection to the street-fighter's co-ax being a .50 cal with an extended barrel, it's just that with a smaller main gun in a relatively large turret, I think something even punchier could be arranged. And if dual feed isn't available then just load it with solid AP rounds: it'll still hit like a .50 cal on steroids and you have the precise, limited terminal effects that you want in street fighting. HE is what the main gun is for in any case. Target a bit less precise, but still too near that school? Fire a short burst.

[rickshaw]

MBT-70's 20mm was purely an AA weapon and faced to the rear.  It had a 7.62mm co-ax.

Designers keep trying to push 20mm co-ax weapons but invariably the end-user rejects them, preferring to stick with an MG, because as I pointed out, the main role of the co-ax is best served by an MG, rather than a cannon.

The Swedes took the idea of a cannon co-ax to the ridiculous when they proposed putting a 40mm co-ax on their indigenous designed Stridsvagn 2000.  The co-ax ammunition was so large it seriously ate into the main gun's magazine space and in the end the sheer expense and the utility of such a arrangement ended up in it's rejection and Leopard 2s were purchased instead (and guess what?  It has an MG for a co-ax...)

[Weaver]

The MBT-70's 20mm only stowed facing backwards: when deployed it was on a rotating cupola. A non-retracting 20mm cupola weapon (similar to the Marder's) was also a feature of early prototype Leopard IIs.

Many AMX-30s went into service with 20mm cannons, as did all Swiss Pz.61s, so the rejection of the end user isn't "inevitable" at all.

The argument you're putting forwards is appropriate to a conventional main battle tank with a large, high-velocity gun whose primary purpose is to engage other tanks, but this thread is concerned with an urban combat/counter-insurgency tank with a main gun reduced in size and power from it's MBT origin, so there should be space and weight enough to spare for a 20mm.

Look at the BMP-3: that manages to get a 100mm low-velocity gun, a 30mm autocannon and a 7.62mm MG in a turret which is far smaller than a Centurion's, yet still with 60 deg of elevation. Given that example, I really don't think that an 80-odd mm low-velocity gun, a 20mm cannon and a 7.62mm MG in a Centurion is that much of a stretch.

[rickshaw]

It isn't and I haven't suggested it was.  My point has always been about utility rather than ability.

There would be nothing wrong with a 25 pdr+20mm+MG mount.  Using a 20mm confers IMHO no added advantage. My preference though would be to be able to cover as many arcs as possible, simultaneously, hence a casemented vehicle with sub-turrets.

The BMP-1 had a 73mm gun.  It's turret was considered a death trap by most observers and it's utility was rather marginal (hence its replacement with a 30mm cannon on the BMP-2).  The Soviets have long tried to cram far too much into much too small a space without ergonomic considerations interfering.  The BMP-3 carries that tradition on.

[dadlamassu]

Multiple gun mountings have never been particularly successful with crews under the stress of combat situations making the decision to shoot which gun at which target has been a great problem.  So yes such things are feasible but not particularly useful in battle.  In this case a short 20pdr may not be the best option but it might well be all that is available.  However, if a more useful street fighting weapon was available (like the 25pdr) or even the old 95mm howitzer from the CS versions of the Churchill then that might be used instead.  There might even be a few of the 105mm guns from the Shermans still lurking about on the market. 

It might even be feasible to mount a 20mm Polsten gun or twin MMG in an armoured mounting on the commander's cupola.

For close in all round defence I doubt multi-turrets (other than on the commander's cupola) are viable in the time period so I'd go for multiple grenade dischargers.

[Weaver]

Multiple gun mountings have never been particularly successful with crews under the stress of combat situations making the decision to shoot which gun at which target has been a great problem.  So yes such things are feasible but not particularly useful in battle.  

All tanks have multiple weapon mounts: main gun, co-axial MG, cupola MG, smoke dischargers, hull MG (in past times) and in some cases a 60mm mortar (Merkava). Tank crews don't seem to have any more problems chosing which one of these to use on which occasion than do those of MICV crews that have autocannons, ATGWs and multiple MGs. As long as the weapons address clearly different target sets then there doesn't seem to be a problem, and I think that would continue to be the case with a low-velocity large-calibre gun and an autocannon. It's mostly a matter of clear and correct training.

[dadlamassu]

All tanks have multiple weapon mounts: main gun, co-axial MG, cupola MG, smoke dischargers, hull MG (in past times) and in some cases a 60mm mortar (Merkava). Tank crews don't seem to have any more problems chosing which one of these to use on which occasion than do those of MICV crews that have autocannons, ATGWs and multiple MGs. As long as the weapons address clearly different target sets then there doesn't seem to be a problem, and I think that would continue to be the case with a low-velocity large-calibre gun and an autocannon. It's mostly a matter of clear and correct training.

I think you misunderstand me.  I used "multiple" to mean several guns on one mount.  Using the OED definition of "multiple", adjective, having or involving several parts, elements, or members.  Also "several" from the OED definition of "several", determiner & pronoun, more than two but not many
In this case a low velocity gun/howitzer, an automatic light cannon and a machine gun all mounted together. 

I did not intend it to mean "many" weapons on different mounts.  Using the OED definition of "many", determiner , pronoun , & adjective a large number of.

Sorry for the lecture and any confusion caused.

For example a FlakPanzer IV Wirbelwind has a multiple gun mount (quad 2cm Flak 38) and a hull MG in a single mount.  The Merkava has a main gun mounted with a co-axial MG, 2 more single mounted MGs, a single mounted 60mm and also sets of multiple smoke grenade dischargers (e.g. 2x6 on the Mk3).  There are a few variations depending upon exact model. 

Incidentally smoke dischargers (as opposed to grenade dischargers) are counter surveillance measures not weapons.  Admittedly they do have a limited anti-personnel value but that is not why they are there.

The problem on the battlefield is that you do not have a lot of time to decide on target priorities, ammunition type, weapon selection for the very brief time that a target is visible.  The more choices you have the slower you are.  If you are slow the other chap will get his shot in first.  Keeping it to one heavy and one anti-personnel makes choices easy.  That is probably why guns are mounted that way on tanks.

I agree that training is a great determinant of performance having spent 41 years training for and on operations.  In that time I've seen the results of smaller forces of well trained highly motivated troops overcoming larger, less well trained and significantly less motivated forces.  However, our basic tenet has always been to keep the drills simple so that the soldier when he is uncomfortable, tired, very cold (or hot), hungry, thirsty and confused can still survive to operate his weapons, follow his orders, make decisions, identify, acquire and engage targets with a first round kill.  The fewer things he has to do the better his chances.

[Weaver]

Whether they're on one mount or not, the fact remains that the crew of a Merkava have to decide how to deploy the range of weapons at their disposal under the high-pressure circumstances you describe:

Main gun
Co-axial 7.62 MG
Over-barrel 12.7mm MG (sometimes fitted)
Cupola MG (higher elevation range than the co-ax and independent rotation)
60mm mortar (points with the turret but has totally different ballistics)

Again, how do the crew of a Bradley with TOW, 25mm and 7.62mm all (effectively) on the same mount cope?

[dadlamassu]

Whether they're on one mount or not, the fact remains that the crew of a Merkava have to decide how to deploy the range of weapons at their disposal under the high-pressure circumstances you describe:

Main gun
Co-axial 7.62 MG
Over-barrel 12.7mm MG (sometimes fitted)
Cupola MG (higher elevation range than the co-ax and independent rotation)
60mm mortar (points with the turret but has totally different ballistics)

Again, how do the crew of a Bradley with TOW, 25mm and 7.62mm all (effectively) on the same mount cope?

The crew does not decide how to deploy the weapons - the commanders do because they have the best optical equipment and they are there to command the tank crew in line with their orders.   

The link is to the manual for the M-60 http://www.cgsc.edu/carl/docrepository/FM17_12_1964.pdf just one of many available.  The responsibilities of the crew and various commanders are gone into in some detail.  There is much more detail than I am willing to go into here.

Anyway - we are well off topic. 

[Weaver]

Well if you're going to be that pedantic it was YOU that started talking about "crews" making decisions:

Multiple gun mountings have never been particularly successful with crews under the stress of combat situations making the decision to shoot which gun at which target has been a great problem.

What none of this nitpicking has addressed is the basic point: you're claiming that a tank with a main gun, an autocannon and an MG would be too complicated for the crew to operate because they'd have to decide which of their several weapons to use. I'm saying that it wouldn't make a difference because they already have a suite of different weapons to choose from.

Incidentally, how do you think the crew of an M3 Grant managed?

We are on-topic because this started when I made the comment that a 20mm would be a useful addition to a street-fighting tank and we've been arguing about the feasibility/utility of that ever since.

[rickshaw]

Incidentally, how do you think the crew of an M3 Grant managed?

An interesting question.  I'd suggest they didn't.   In the Desert, the Grant's 37mm was essentially useless and for the most part ignored.  It was the 75mm which was the main weapon of the vehicle and the one on which the crew concentrated.   It had the range and the stopping power to engage enemy tanks.   As the 37mm also required the tank commander to act as loader, it was never popular as using it prevented him from performing his primary duty of commander and controlling the entire vehicle as a fighting unit, designating targets and directing the driver.    In the Jungle the 37mm had marginally more use, as an APers weapon, firing canister and HE but it was still the 75mm which was the main weapon.  I suspect the 37mm was used but more than likely serviced by the gunner himself, rather than distracting the commander from his main duties.

Forcing the commander to load a weapon is always a bad idea and for the RAC was always considered sub-optimal.

The 20mm is, as I keep pointing a weapon which brings with it a series of problems, as well as advantages in urban warfare.   Personally, my whole criticism of it's use would be on the basis of it simply being "too much" in an urban environment.  It could provide a useful "half-way house" I acknowledge, between the BFG and an MG but I think a HMG can do the same job without the attendant problems of potential "collateral damage".

No one is, I believe disputing that it isn't possible to have a co-axial 20mm.  We have examples of that but as I've pointed out, invariably while vehicles were designed in that way, the end-users didn't like them and reverted to MGs instead.  They obviously felt that a lighter calibre weapon with a higher rate of fire is more useful and as they're the ones with the experience of the matter, I think we have to accept their viewpoint.

However, as this is whiffdom, there is nothing stopping you from creating what you want and it could have a 20mm gun.  It could have a "pulse rifle in the 40 megawatt range" if you so desired.    All you need to do is build it and I for one would admire it.   

[Weaver]

No one is, I believe disputing that it isn't possible to have a co-axial 20mm.  We have examples of that but as I've pointed out, invariably while vehicles were designed in that way, the end-users didn't like them and reverted to MGs instead.  They obviously felt that a lighter calibre weapon with a higher rate of fire is more useful and as they're the ones with the experience of the matter, I think we have to accept their viewpoint.

Actually, that's not strictly true: the AMX-30 went into production with a 12.7mm co-ax in 1966 then switched to a 20mm in 1972. You also have to look at why the 20mm was dropped. In the case of the Swiss tanks, it was in order to make room for gun stabilisation gear and fire control black boxes in what was a particularly small turret, not because of any dissatisfaction with it's combat capability/utility. In most of the cases where it's been dropped during development, it's because it was an easy target for cost-cutting measures.

The rate-of-fire and ammo situation is not as clear for the AMX-30 as you might think:

12.7mm MG (initial fit): 485-635 RPM, 600 ready rounds, reserve: unknown
20mm A/C (preferred fit) : 720-900 RPM, 480 ready rounds, reserve: 550
7.62mm MG (international norm) : 650-1000 RPM (FN-MAG), about 600 ready rounds and 2000 reserve (assuming the co-ax would have about the same ammo supply as the cupola MG)

At the end of the day, a single-feed 20mm with solid shot is just a bigger HMG. I think it has value against enemies in tall buildings or behind thick walls. However if there was a significant disadvantage to using it, I wouldn't cry to see it replaced by a long-barrelled 0.50 cal. The key point is that I want my urban tank to have a high-angle, flat-trajectory small calibre weapon that can take out a sniper in a window without demolishing half the building or putting a round though every window next to it.

[Scotaidh]

I've actually thought that a Lee/Grant would be just the thing for urban warfare - tall, roomy (comparatively) interior, and the commander had a very high point of view ...

I'd replace the original weapons with more modern ones, of course - the 75mm with the cannon used in an A-10 or perhaps a RARDEN cannon; the 37mm with a Vulcan (20mm rotary cannon); and, on the Grant, the top MG with a mini-gun. 

[rickshaw]

In it's CDL variant, it was found to be ideal for quelling civil unrest in India.  The searchlight turret backed by the hull sponson mounted gun was apparently very intimidating.  The point being though, they actually did away with the turret mounted 37mm weapon.