ROF of AT guns

[ASL Veteran]

I can make a few comments about the various marks of 88 Flak from Osprey's "88mm Flak 18/36/37/41 & PaK 43 1936 - 1945"

For the FlaK 41 the horizontal sliding breech now used a ramming mechanism that assisted in loading the shell (which apparently was a larger shell than on earlier 88s). It also had a separate firing circuit for use when firing against ground targets. It further states that "In theory a well trained crew could fire 20 rounds per minute, but for all practical purposes this was never accepted battle procedure.

Interestingly it says that the FlaK 37 wasn't used in a ground role because it had a pretty advanced fire control system:

The Funkmessgerate also contained information about the site of the gun and ballistic data on the type of shell and fuse. Once the position of the aircraft had been calculated, the Funkmessgerate would compare weapon data and calculate the optimum time to fire, so that the shell intercepted the target at the right time and height. The crew inserted the nose of the shell into the gun's fuse setter which automatically set the time fuse of the high explosive round to detonate at the correct height once fired.

there is a picture in the book with the shell sitting nose down in what looks a little like an automobile cup holder.

The ROF for the FlaK18 is listed as 15 RPM

For the PaK 43/41 there is the following info regarding ROF:

The larger shell weighed 23 kg, and produced dense clouds of smoke on firing, which in cold, calm weather conditions could linger around the site of the gun's position. This not only betrayed the position of the weapon, but also obscured the gunner's sight when traversing the weapon to engage the next target. It was recommended, therefore, that rates of fire be kept to under 15 RPM in order to prevent build up of vibration in the barrel. However, no gun crew could ever expect to fire 15 rounds per minute, especially given the fact that the new shells weighed almost twice as much as the original 88mm shell, and ten rounds per minute was the given specification.

The book also has a brief discussion about the 88s in the Tigers and various SP guns, but never mentions a ROF figure for them.

[JasonC]

Andreas - the reason 2.5 sec vs. 3 sec doesn't matter is because you won't actually get either of them. As I said, other minor factors will make more of a difference in the actual ROF you will see than that theoretical maximum of the guns, because the figure itself is so low and the absolute difference between them is so low.

Another fellow presented evidence that in practice 10 per minute was more realistic with the supposedly faster of the two, which is perfectly plausible. And to me shows that ascribing any real world importance to theoretical rating difference of 20 vs. 25 per minute is ridiculous.

Londoner - I thought I had addressed the question of why towed guns need larger crews, but if I wasn't clear before I will expand on it. The biggest reason is they need an "ammo detail" to handle moving and prepping shells. You don't stack 50 rounds 3 feet from the piece. Only one guy is doing the actual loading at any given moment.

(Another is aiming, the gunner, and a commander is directing the crew and ID targets through field glasses or what not. On some pieces another man elevates and depresses, with the gunner handling only traverse).

They can switch off the guy doing the loading if he gets tired, to be sure. But he isn't going to get that tired in anything like a CM tactical engagement time scale. Hours and tons will exhaust gun crews, not pounds and minutes.

What are the other members of the crew doing? Ammo detail. That means they fetch the shells from wherever they are piled, up to right next to the gun. To minimize delay in that process, you want several people doing it, in a relay. So the loader has a ready shell next to him as soon as he is ready to load it. If the shells haven't been prepped yet (fused, etc) then other members of the ammo detail back by the shell pile are doing that.

You don't need these other people in an AFV, because the AFV hauls the shells, holding them a few feet away from the gun at all times. Shells are prepped before the AFV heads out into action, and stowed in easily accessible racks. Extras are stowed in less accessible places, like around turret or in the floor, varying from AFV to AFV. (The biggest ones typically go in the floor). There is no complexity in getting a round out of the racks and into the gun.

YankeeDog - Yes it would be great if the depth of ready racks were modeled, as well as the overall ammo capacity of the vehicle. It is quite small for some types, especially bigger caliber guns (e.g. Russian 122mm).

As for the question of who fishes out extra shells when the ready racks run dry, the loader does first of all, and if he needs help (which is common enough) then the gunner is the one who would help. The driver and radio-MG operator are not in the turret or gun compartment. The commander is up in his high seat, and would just get in the way - there is no room for a third person on the floor of the turret along with the other two crewmembers, an opened floor hatch, and loose (meaning, not pinned into racks) shells.

Could you do it while moving? Not a chance. I don't care if you were doing only 10 mph and on an autobahn. It would be crazy - you are lifting fuzed shells with both hands out of the opened floor of a swaying vehicle.

The normal thing would be to go to some turret down location (full defilade I mean) and halt, and then the loader and gunner would open the floor hatch. One is down on his knees and picks the shells out and passes them up to the other, who is standing, and who places them in the empty ready racks.

They'd fish out enough to get at least the racks on one side of the tank full again; if they have a lot of time all of them. Then close the floor and get back to their fighting positions. It would take around 2-3 minutes.

Some tanks, especially with smaller caliber guns, had rear turret stowage instead, high up. One guy can do that, because he is standing the whole time and just lowering the shells. He does have to reach and do them one by one, but it is definitely easier and probably faster than big shells out of the floor.

[ June 12, 2002, 07:43 PM: Message edited by: JasonC ]

[YankeeDog]

Jason -

Thanks for your response. It mostly confirmed what I already suspected, but it's good to get verification from a knowledable source.

Your comments about ready racks further solidify my opinion about "burst" ROF for tanks (i.e., a higher ROF after range and bearing have been found on a stationary target). Namely, that such an increase in ROF should probably not be modeled unless ready-racks can also be modeled. Otherwise, the tank would be able to maintain a high ROF for an unrealistically long period of time against, for example, an area fire target.

Cheers,

YD

[Thin Red Line]

Originally posted by YankeeDog:

Interesting subject. Thanks to JasonC and other knowledgable grogs who have posted comments here.

Yes , thanks, now i understand better why my opponent lost 12 tanks in 1 turn just after i've unhidden 3 elite 88s and 1 elite Pak 40

[StellarRat]

Can we draw some vague conclusion about the importance of tank ROF in the fact that the US has never used a mechanical loader in it's tanks? It seems to me an autoloader would be able to sustain a very high rate of fire (provided it didn't jam.) My bet is that aquiring the target takes more time than anything else.

[Michael Emrys]

Autoloaders can actually slow the rate of fire if they require the gun to be relaid for every shot (cf. the T-62).

There are other reasons usually cited for having a human loader though: an extra pair of hands to help with routine maintenence; an extra pair of eyes when traveling through "injun country", etc.

Michael

[Redwolf]

The autoloader in cold-war Soviet tank designs is to save a crewmember. Which is foremost done to keep the tank small and flat, and only secondary to get enough men for all that cheap tanks.

The rate of fire is assumed to be two third to one half of what a western tank can do, and the autoloader is pretty dangerous in terms of stuffing crewmembers with loose clothing into the breech or nothing at all.

The whole thing gets worse by the fact that Soviet tanks shoot HE, compared to the Western designs that often only have SABOT and HEAT. The Western tank can eliminate an armored threat suddenly appearing while fighting infantry on the fly. The Russian tank has to fire the HE for no gain and do the slow autoloader reload before being able to shoot antitank ammunition.

[Paul Lakowski]

Originally posted by redwolf:

The autoloader in cold-war Soviet tank designs is to save a crewmember. Which is foremost done to keep the tank small and flat, and only secondary to get enough men for all that cheap tanks.

The rate of fire is assumed to be two third to one half of what a western tank can do, and the autoloader is pretty dangerous in terms of stuffing crewmembers with loose clothing into the breech or nothing at all.

.

Ehh ROF of Russian tanks is about 1/2 to 1/3 that of comparable western models.

[Redwolf]

Originally posted by Paul Lakowski:

Ehh ROF of Russian tanks is about 1/2 to 1/3 that of comparable western models.

Well, it probably depends on how you count. The autoloader rate is constant, but the human one has "bursts" versus continued. Some of the very low numbers for Soviet tanks include an assumption that the gunner takes longer to aim (Conscript, no practice etc.).

In any case, the autoloader does not raise the ROF.

[JasonC]

On the subject of autoloaders, the Russian ones have certainly been less than successful. But the US has considered the idea, though not for MBTs that I know of. The Crusader was supposed to use an autoloader, indeed to be fully automated as to the whole loading and firing sequence.

The design specs called for a roughly doubled ROF (compared to surge ROF of the M109, which is rated 2-3 rpm but can in practice be pushed to 4-5) to 10-12 rounds per minute for the first 30 shells (which are one ammo "module" in the autoloading layout). These are 100 lb shells with seperate loading ammo, that need hydraulic ramming to seat the shells properly in the tube, between shell and powder insertion.

So obviously there is more room for sophisticated machinery to improve the process, which is relatively complicated and involves large weights. Whether the thing will ever actually be built is now up in the air, with the DoD wanting to cancel it, while congress and many generals still want to keep it.

It is noteworthy that the most they expect from the latest high tech system for the biggest shells is an increase to about the ROF humans can achieve in oractice for smaller cannons. There doesn't seem to be a lot of wasted time in the way humans load middling caliber shells (meaning 75-122mm).

By the time you are down to 5-6 seconds per round, further improvements are apparently pretty hard to come by. An automatic feed would seem to be the only obvious way of making significant improvements beyond that, but that in turn would seem to require an entirely different design of things like the breech. The designs used for smaller autocannons can't scale up to big guns because of this issue.

Mid sized and larger cannon need very heavy breech blocks the seal very tightly to prevent rearward venting of the power of the explosion in the tube. The tube obviously has to open somewhere to be loaded. And wherever that is, you will need some heavy and elaborate mechanism to close off the hole you must open to load.

With small cannons, you can load from the side of the barrel, and close the firing chamber with relatively thin material. But no such thin cover could withstand the explosive force needed to drive big shells. Loading from the rear obviously requires several additional steps, and because the recoil is along that axis you can't have any machinery "living there". Whatever does the loading has to move aside for recoil, and back into place.

It is also questionable whether ROF improvements beyond one round per 5-6 seconds would matter much for large caliber guns. Practical ammo loads with relatively big shells top out around 50 rounds. At peak ROF, that means even the reachable level exhausts the practical ammo supply in 4-5 minutes. No battlefield resupply system could possibly top off every weapon system that fast.

While individual duels can be shorter than that, battles never are. So many rounds aren't likely to be needed to KO targets visible at the same time anyway. And if so many shots were needed to do so, that implies much greater room for improvement by focusing on accuracy (e.g. smart terminal homing) or shell lethality (ICM cluster munitions e.g.) than by focusing on rate of fire.

[Paul Lakowski]

Originally posted by redwolf:

</font><blockquote>quote:</font><hr />Originally posted by Paul Lakowski:

Ehh ROF of Russian tanks is about 1/2 to 1/3 that of comparable western models.

Well, it probably depends on how you count. The autoloader rate is constant, but the human one has "bursts" versus continued. Some of the very low numbers for Soviet tanks include an assumption that the gunner takes longer to aim (Conscript, no practice etc.).

In any case, the autoloader does not raise the ROF.</font>

[Michael Emrys]

I find myself wondering about heat buildup as a limiting factor in RoF, especially of larger guns (100mm and up). The barrel and firing chamber need to be massive enough to serve as adequate heat sinks until the heat can be dissipated. Further, in order to avoid warping, the barrel needs to remain at as constant temperature as possible.

As for rapid dissipation of heat, I haven't so far noticed much in the design of big guns to indicate steps in that direction, no cooling fins or special alloys.

In any event, all this is especially problematical when we get to guns mounted in vehicles for a number of reasons. There weight is at a premium, so extra-heavy forgings are out. Space inside vehicles is also at a premium, so cooling fins are out too, even if designers were inclined to employ them, which as I said I have found no evidence of. Lastly, most enclosed AFVs have had poor air circulation and cooling until relatively recently, which would inhibit heat dissipation as well.

Bottom line: you can have a high RoF burst, but it better be a short one.

Michael