Why did the Russians built the su76's?

[stikkypixie]

I can understand why they built the su85, su100, su122, su152 because they needed the firepower quickly and couldn't wait until a tank with that gun was developed but the 76.2 mm on the su76 was standard on a T34 not? So why the need for the su76.

[flamingknives]

AIUI, the SU-76 uses the chassis of theT70 light tank, which was rapidly becoming obsolescent by the time it (the SU) was introduced.

That chassis is therefore upgraded from a 45mm gun to a 76.2mm gun.

[Gaylord Focker]

Turretless vehicles were easier and faster to assemble/manufacture and used less recources to create than full fledged tanks.

A Mobile/armored 76.2mm gun has some advantages over the carriage drawn gun.

[ October 12, 2003, 05:19 PM: Message edited by: Gaylord Focker ]

[Pzman]

At first it was going to be a tank destroyer, but then they found that the 76.2mm gun was no longer effective in that role it was used as direct artillery support for infantry. Since Germany's armor was so thinly spread by late 1943 - early1944 the thin armor of the SU-76M wasn't a problem. It should be noted that it was the 76.2mm ZIS-3 Gun not the same gun as on the T-34/76. The ZIS-3 gun was slightly less powerful IIRC.

[ October 12, 2003, 06:30 PM: Message edited by: Panzerman ]

[JonS]

Why did they build the SU-76? Easy - they were thinking of Kip.

[JasonC]

Light tank chassis production lines existed. 20mm and 45mm main armament tanks (T-60 and T-70) were not useful in the second half of the war. So they kept the lines in production and upgunned those vehicles, sacrificing a turret. The Germans were doing the same thing with their Pz II and Pz 38 chassis production.

The ISUs were based on IS chassis, which itself replaced KV production after a point. The SU-152 was based on a KV chassis. The SU-85, 100, and 122 were based on the T-34 chassis. Production of each of these types meant fewer IS-2s, KVs, and T-34s. Production of SU-76s did not. Only T-60 and T-70 production was given up to have them.

Used in independent "regiments" of 20-24 SUs, they operated as self propelled AT and as self propelled arty. They filled the role the Germans used Marders and Wespes to perform. Those German types were also based on their light tank chassis. Armor protection could be sacrificed, a turret could be sacrificed, but a real gun could not be. Anything in armor and on tracks, with a decent gun, was useful.

[Guest Mike]

And of course the T70 lines couldn't be quickly or easily converted to produce anything bigger like T34's - the light tank production lines were based around automotive factories rather than "real" tank plants.

[YankeeDog]

My understanding is that the factories used to build T-60s, T-70s, and finally SU-76s lacked the heavy equipment necessary to build larger chassis, and so converting them to build T-34s would have been especially difficult.

Jason - I have read that the SU-76, and indeed Russian SP guns in general were not really capable of performing as true SP Arty like the Wespe or Hummel as they lacked the proper sighting and elevation mechanisms to do so. Is this incorrect?

Cheers,

YD

[stikkypixie]

thanks for the great replies guys

my day can't go wrong anymore, knock on wood

[Zitadelle]

The provided comments are right on target. The factories that were used to build the T-60, T-70, and SU-76 were automotive factories and were not tooled nor had the heavy lifting equipment necessary to build tanks. Since, re-engineering the factories to build tanks required too an extensive effort, the Russians decided to switch to the building of the SU-76 when the T-60/70 finally were proven as obsolete.

Unlike the StuGs, the SU-76 was not developed nor deployed as an AT assault gun. The Russians developed the AFV solely in a direct fire support role. Furthermore, YankeeDog is correct that the SU-76 was not equipped with indirect fire sights and appropriate elevation mechanisms.

[Andreas]

The other element is of course the gun. The way I understand it (Kip knows more about it than I do), the Zis-3 was a fabulous gun, and the Soviets were churning them out (>56,000, according to this article by Jason Long. So, once you have so many field guns that you can equip any rifle division twice over and then have some left for barter, what do you do with them? Make them self-propelled.

[Guest Mike]

SU-76's were originally intended to have an aT function, but it was rapidly found that they weren't much use for that - teh gun was to mediocre and the armour wasn't thick enough.

One of the incentives for designing the SU-76 was the shortcomings of the ZIS-30 - the 57mm gun on the Komsomlets tractor used in small numbers in 1941 - a great AT gun that could kill anything the Germans had at the time.

The SU 76 was envisaged as a successor to this that would also provide a useful HE support function.

See http://www.battlefield.ru/su76.html

[MikeyD]

When it comes to cannons, size does not always matter, especially for infantry support.

The U.S. 75mm gun Sherman gun is widely considered to have been the best all-around gun of the war, despite its shortcomings in hole-punching abilities. That's because of its VERY wide variety of rounds, its accuracy, and its fat HE round (much better than a Panther or 76mm gun Sherman's HE round).

The Russian 76.2mm gun was the Russian version of the 'workhorse' all-around useful medium-pressure gun.

[Redwolf]

MikeyD, you probably speak of the semi-long 75mm.

The 76mm was overall lousy.

And the main reason why so many Shermans were built with the medium-velocity 75mm is that they had a huge requirements for number of rounds to be fired from one barrel, although as you say the HE round was also more effective.

[JasonC]

"The U.S. 75mm gun Sherman gun is widely considered to have been the best all-around gun of the war"

...

by drunken jingo trolls in la la land, perhaps.

Anyone ever heard the words "eighty-eight"?

[Wisbech_lad]

Have to agree with JasonC. The 88mm British "25pdr" was a great gun...

[HeinzBaby]

..just curious, we know the 25pdr was a great Field Gun with secondary AT capability but what was it's ROF?, [it did have seperate shell and case] and the 88 could fire up to 20 rds per min, depending on its crew...

[argie]

The 25 pdr hadn't separate shell and case.

I don't remember the ROF, but was pretty high, plus being stabilized with a wheel that helped fast fire fan changes.

[HeinzBaby]

Sorry Ariel, I'm getting old, drink to much red and memory is fading...but I did find this http://www.42regt.abelgratis.co.uk/guns/25pdr_text.html

[argie]

Maybe I'm getting older than you, as I have this image on my head of a 25pdr being reloaded with fixed ammo :eek:

[Andreas]

Originally posted by Ariel:

Maybe I'm getting older than you, as I have this image on my head of a 25pdr being reloaded with fixed ammo :eek:

You must be really scared about the bang when they decide to fire it eventually. At least they have a good field of fire.

[JonS]

There is also this on the 25-pr.

It used seperate loading ammo. In some photos of the gun you'll see a guy with what looks like an overly large drill cane with a blunt end. It wasn't used to beat the crew if they cocked up - it was in fact used to ram each projectile as it was loaded to ensure it was properly seated before the cart-case was loaded in behind it.

The official "Intense" rate of fire was 5rnds/min, but crews would often acheive on the order of 12 rounds per minute when engaging targets with no specified rate. A Canadian crew was timed just south of Caen in August 1944 and got away 17 rounds in 60 furiously busy seconds.

Regards

JonS

[Private Bluebottle]

Originally posted by Ariel:

Maybe I'm getting older than you, as I have this image on my head of a 25pdr being reloaded with fixed ammo :eek:

A brass cartridge case into which the charges were fitted before loading was used. The projectile was loaded seperately. This allowed flexibility in the number of charges used (they could be removed/added as required) allowing a great variation in velocity and range in the artillery role.

Its ROF is given as 5 rounds a minute sustained although Blackburn in his books on NW Europe makes the point higher rates of fire were possible for short periods of time. The reason why the German 8.8cm guns had a much superior ROF was becuase (a)they're AA guns and therefore, designed to sustain a high ROF and ( have a fixed round.

[ October 16, 2003, 08:29 PM: Message edited by: Private Bluebottle ]

[Guest Mike]

I beleive the AT round for the 25 pdr was fixed wasn't it?

The 2-part round was necessary to give full coverage of all ranges when firing indirect by using variable charges.

[JasonC]

Separate loading ammunition. Means the round is one thing, and the powder bag is an entirely different thing. First the round - which must be fuzed i.e. have a headpiece screwed on that sets it off when it hits - goes in the breech. It is rammed home. Then a powder bag is placed behind it. Breech is closed and powder is fired by a primer, sending the shell to the target. Used when the shell is heavy enough already, and to vary the powder charge to reach different ranges. Examples - 155mm and larger artillery.

Semi-seperate ammunition. Means the round is all that goes in the tube. But the top of the round unscrews, and separate bags of powder can be removed from the round to change the range. The powder comes in a number of bags held together by cloth strips. You break the strips off to remove come of the powder for a less than full charge. This is called "cutting the powder". After cutting the powder, the nose of the shell is screwed back on. It is then fused - a fuse added to the tip. The round is now ready for firing.

Once prepared in that fashion, however, a semi-separate ammo round is the same as a "fixed" ammo round. Meaning, it is the only thing that goes in the breech and does not need to be rammed.

Examples - Brit 25 pdr, US 105mm. Medium caliber tube arty that must vary its range, in other words.

Fixed ammunition - the round comes from the factory with only one size powder charge. The round is sealed, and the gunners do not fiddle with it other than to add the fuse. Examples - most main tank guns in WW II, 75mm and lower calibers even in field artillery.

Semi separate ammo requires an ammo prep operation when firing a large number of shells. (All ammo types require some of this e.g. to remove from packing material, add fuses, stow properly, etc). But this does not slow loading. The rounds can be prepared well ahead of the actual fire mission. Once prepped, they can be loaded as fast as fixed ammunition.

Separate loading ammo can also be fuzed ahead of time to save loading time. And the powder charges can be "cut" to the right size. But one still must go through several additional movements to load and fire any separate loading piece. The shell has to be rammed up the breech far enough to allow room for the powder charge behind it. This considerably slows the maximum rate of fire, compared to fixed or already prepped semi-separate ammunition.

Incidentally, it is still possible to get off 3-4 and sometimes even 5 rounds per minute with separate loading ammo and 100 lb 155mm shells. Loaded by a single man, just working hard. This is certainly tiring, but tiring as working out in the weight room is tiring - over a time scale of an hour, not of a few minutes.

Incidentally, "sustained" rates of fire are mostly set by the characteristics of the gun, not by loading skill or speed. The issue is heat. Barrels get very hot when round after round is fired through them rapidly. Hot things expanded marginally. Hot heavy long things can even droop marginally. If you over work guns you risk "burnt out barrels" - you get "short" rounds created by excessive "windage".

You also risk "burst gun" incidents, many of which are actually caused by premature detonations induced by embers inside a barrel, and the like. You can't simply cool the guns e.g. by pouring water over them. That can crack the metal, as it cools the outside but not the inside. You can and do swab out the breech trying to extinguish embers. But you can't remotely cool a tons weight of metal that way.

I hope this clarifies things.

[ October 16, 2003, 11:23 PM: Message edited by: JasonC ]