Sunday 21 December 2014

IS-3 Reloads

If you've read my article on the history of the IS-2 and IS-3 tanks (and you probably should), you may remember a mention that the IS-2 can fire at a rate of 4-6 RPM. Some people have questioned this statement. How can a tank using such huge shells fire that quickly? If it could fire so fast, why could the IS-3 and IS-4 not do the same? The answer, as always, is standards.

I've written about rate of fire tests previously, in an article on the KV-9 and an article on the KV-100. Both reveal a critical component of Soviet testing. The KV-9 can fire as fast as every 12 seconds, but the rate of fire recorded in the test was only 2 RPM! The KV-100 test, which is invalidated due to all shells being loaded from the turret bustle, hints at the reason for this. The rate of fire recorded by the Soviet standard is using all ammunition racks, even the most inconvenient ones. This is illustrated well in Yuri Pasholok's book SU-152 and other SPGs on the KV tank chassis. Google around for the rate of fire of a SU-152, and you might find numbers ranging from 1.5 to 2 RPM. However, during trials, loading a shell from the most convenient rack took as little as 16 seconds (p. 132) and firing off the 10 most conveniently placed shells (half of the vehicle's ammunition) could be done with rate of fire of 2.8 RPM (p. 133). The rest of the rounds would take longer to load, but there were few instances where it would be necessary to empty the entire ammunition rack in one go. The loader would refill the ready racks when the fighting died down a little, and would be able to fire quickly once more in a few minutes.

Hopefully, that explained the "how can an IS-2 fire so fast" question. Now, for the next question. Why couldn't the IS-3 match the rate of fire of its predecessor? The short answer is "sure it could". The Domestic Armoured Vehicles series of articles from the Tekhnika i Vooruzheniye issue #11 for 2012 describes the rate of fire testing on an IS-3.

"...from June 20th to July 12th, 1951, trials were held, the results of which showed that the average aimed rate of fire with a trained loader could reach 3.6 RPM (the technical requirement was 2-3 RPM). The average cycle lasted 16.5 seconds and consisted of removing a shell from the brass catcher (2.9 seconds), loading a round (9.5 seconds), correcting the aim and firing (3.1 seconds) and the recoil brake returning the gun to the firing position (1 second).
...
The trials evaluated the possible approaches to ammunition racks of the gun and tested methods for loading it. The most accessible were the 17-shell rack around the turret ring, positioned towards the loader next to the fan, and the five-round rack located on a frame attached to the central contact device, as they allowed for the gun to be loaded in any position."

1. An HE shell is taken from the 17-round turret rack.

2. Another HE shell is taken from the 17-shell turret rack.

3. Propellant is taken from the 5-round rack.

4. The sixth HE shell is taken from the 17-shell rack.

5. Propellant is retrieved from an ammunition rack next to the engine compartment bulkhead.

The test and photos reveal a lot about the details of the test. For instance, we can see that loading the gun takes only 9.5 seconds, the rest, aside from the gun's return to its initial position, can be skipped if you're testing maximum rate of fire, instead of maximum aimed rate of fire. Just dumping shells downrange and worrying about the brass later can already obtain a rate of fire of 6 RPM. However, the 9.5 second figure is the average figure, for all racks. As you can see in the photo, bending down to get a 122 mm shell from the bottom of the fighting compartment can be really inconvenient. Meanwhile, the loader doesn't have far to reach in order to get to his closest ammunition. The book doesn't say how much faster loading from the turret as opposed to the hull is, but with ammunition this heavy, it has to be noticeable. It should be pretty clear that even with aiming, the IS-3 can fire much more quickly than the rate it was required to achieve according to its technical project.

Edit: Here's a little tidbit that I found, Mikhail Svirin himself writes: "The practical rate of fire [of the IS-2] in place was up to 5 RPM, on average 2.5 RPM, 1.5 RPM in motion."

15 comments:

  1. This comment has been removed by the author.

    ReplyDelete
  2. I dont see any reason why does reload should take more than 20 seconds with this gun. If I am enough strong to pick up shell and propellant I have to put to the breech as fast as I can. On the one forum there was guy who stated that rate of fire doesnt depends on physical work but maximum allowed rate of fire by stated gun. And the maximum allowed rate of fire of this gun is 6 rpm according to him. But I am sceptic about it because I cant imagine the situation in which loader should waiting before reloading the gun during intense fight with enemy. Are there some informations about this ?
    But thank you for great article.

    ReplyDelete
    Replies
    1. Are there some informations about this?

      "if you're testing maximum rate of fire, instead of maximum aimed rate of fire."

      The 6RPM for the IS-2 does only consider the sustained loading with firing, not the sustained loading with firing at the obligated aim (target acquisition). That's why the KT and IS-2 have same loading by the Soviet standard.

      The sustained loading, aiming and firing is given by 2-3 rounds for the IS-2 with split-type ammunition and semi-automatic drop breech as average in combat (source: Артиллерийское вооружение советских танков 1940-1945 ) while the germans archived 8 rounds under same requirement with the KT (source: ISUM 29, GS I, 21st Army Group, July, 1944)

      In sign for interest, the Panther and Tiger could fire 3-4 times of every 1-1,5 shots of the IS-2. Have look here: http://tankarchives.blogspot.cz/2014/06/first-is-2s.html

      Delete
    2. According to EE, Kingtiger and is-2 shoot just as fast.

      Delete
    3. Anonymous said...

      The difference between the initial KV-122s and all the later IS-2s was that the initial KV-122s had basically a barely modified A-19 also called D-25 which had screw breech block, meanwhile all proper IS-2s (both the early and mod.44 hulls) had D-25T semi automatic sliding breech block. The sliding breech block was both much faster to operate and also didn't take up as much space in the turret as the A-19 had "doors" that opened into the space.

      Delete
    4. "According to EE, Kingtiger and is-2 shoot just as fast."

      I don't see where I said it otherwise:

      "The 6RPM for the IS-2 does only consider the sustained loading with firing, not the sustained loading with firing at the obligated aim (target acquisition). That's why the KT and IS-2 have same loading by the Soviet standard."

      6RPM for IS-2 and 6 RPM for KT.

      Even Peter explains this:

      "if you're testing maximum rate of fire, instead of maximum aimed rate of fire."

      And gives an example:

      "...from June 20th to July 12th, 1951, trials were held, the results of which showed that the average aimed rate of fire with a trained loader could reach 3.6 RPM (the technical requirement was 2-3 RPM). The average cycle lasted 16.5 seconds and consisted of removing a shell from the brass catcher (2.9 seconds), loading a round (9.5 seconds), correcting the aim and firing (3.1 seconds) and returning the gun to the firing position (1 second).
      ..."



      Delete
    5. Peter = EE = ensign expeldable.
      And who are you? Lol

      Delete
  3. This comment has been removed by the author.

    ReplyDelete
  4. "In sign for interest, the Panther and Tiger could fire 3-4 times of every 1-1,5 shots of the IS-2. Have look here: http://tankarchives.blogspot.cz/2014/06/first-is-2s.html"

    But this is earlie variants which gun had screw breech.

    And yes there is difference between maximum rate of fire and maximum aimed rate of fire but If you are shooting the same target more times (big house or some fortification) the gunner will aim gun on target faster then loader will load gun because he had to just stabilize gun on the target after fire. And there is possible to fire 6 rounds per minute and I would say even more if the loader is skillfull, strong and has asbestos gloves.

    ReplyDelete
  5. "...and returning the gun to the firing position"

    Does this means having to re-calibrate the sight? (but it's only 1 second, so I don't think so)

    That aside, this explains the difference in the loading time of IS-2s in the two competing games; World of Tanks and War Thunder.

    Seems WG based their IS-2s rate of fire on the maximum rate of fire., while Gaijin based their IS-2s rate of fire on the rate of aimed fire

    ReplyDelete
    Replies
    1. As any mechanical device with tolerances, the gun will wobble when a shell is loaded. It wobbles a little bit, but for optimal precision, you still need to re-adjust. Every gun does this, not just the D-25.

      Delete
    2. also, I'm not sure what a 'brass catcher' is (sorry for this, there is much to learn as English isn't my mother tongue) but it seems to work as something to contain the propellant case after firing and the case is ejected from the breach, this means a new round and propellant case can be loaded into the gun even without removing the spent casing from the catcher, correct?

      Delete
    3. Yes, essentially a sack that is hung up to catch ejected casings.

      Delete
    4. Now this brings me to another question.

      How many spent casing can the brass catcher holds before having to remove the casing from the catcher?

      Also, where is the catcher located? Will it be harmful for the loader to remove the spent casing from the catcher after a round is loaded (I mean, having to remove the casing while the Gunner take aim and fire could result in the breach blown back and hit the loader can it not?)

      Delete
    5. I don't know how many casings it can hold. It's located immediately behind the breech, so it's not safe to stick your hand in there when the gun can fire.

      Delete