high velocity and low velocity guns

[malfuriouspete]

Anyone care to explain the purpose of a low velocity gun on a tank? I've heard that low velocity guns were used by tanks that had an infantry support role, such as early Panzer IVs with their short gun barrels and high explosive shells.. but could high velocity guns with HE rounds be used in the same role?

[ww2steel]

Low velocity guns were the standard for the 'large bore' guns pre WW2 (the 75 being considered large bore then). It's simply a howitzer put into a turret. It has the advantage of being less restricive in close quarters combat (woods, urban, etc) because the turret can turn much more easily than a clumsy long gun on a Panther or something. You also have to worry about planting a long gun into the ground when descending a steep trench, poking it accidentally into a building while maneuvering, etc. Short gun tanks are easier to transport. These last few reasons are why you often see tanks that are not in a combat area with the turrets turned to the rear. The short gun of the PzIV was due to an order (I think maybe directly from AH??) that the tanks were not to have an overhang of more than the length of the hull forward the turret.

The BT-XA and T-26A, along with the early T-28 land battleships; the PzIV; etc. were examples of infantry support where armor penetration was not the issue. Getting a potent HE round on target was the issue, and a slow round - with a higher trajectory - can actually be advantageous sometimes (though harder to hit a target with the first round). Also, circa 1938, a short 75 AP could crush nearly anything fielded.

Also consider that these were not intended to be the tank killers. They were capable of destroying enemy armor, but a BT-5 or PzIII with a smaller medium velocity gun was more capable (flatter trajectory makes for better accuracy, you could load and fire a 45/50mm gun much faster, you can carry more of the smaller ammo, etc.).

It was later in the development stage that medium 75s and similar were fielded. This is the point in technology that I personally count as being a WW2 era tank (not so much the gun fitted, but the technology state... I obviously count a PzIIIL as a WW2 tank- barely). The T-34, M3 with the side sponson, and finally the Germans with the PzIVF2. It was finally clear that these specialist tanks were a liability, and without much more consideration a multipurpose tank was created that could perform adequately for both roles.

Hope this helps,

Mike

[Dinodawg33]

Howdy,

The high velocity guns' barrels last (roughly) about 25% of the life of the short/slow gun barrels. Between the barrel cost and the "off the line" maintenance time required to replace the barrel 3-4 times as often is a logistical decision.

US 105mm howitzer

Death Traps by Belton Y. Cooper ISBN 0-89141-814-8

The author explains the 105mm round could be seperated to adjust the amount of propellant charges. Each new round came with 7 bags of smokeless powder. Every 7 propellants used equalled a service round. Army ordinance estimated the service lfe of the barrel to be 7500 service rounds fired at a rate of 4 per minute. However, the gun barrels did not fire near that many service rounds (no specific number given) and the entire divisions 105mm barrels (54 in all) needed immediate replacement. Army ordinance were told, and had to see to believe the 105's were being fired at over 10 rounds per minute.

'Weapons of War' Series: The 25-Pounder in Canadian Service

by Doug Knight ISBN 1-894581-26-1

The 25-lb gun was not the most powerful or longest ranged weapon on the battlefield, but Doug points out where its strengths were and why it was popular. One point he makes is the gun fired a projectile only slightly smaller than the US 105mm (25 pounds versus 33 pounds) to the same range and with a smaller and more easily handled gun. The 25-lb barrel was also more long-lived. Artillery weapons' life expectancies are based on how many "full charge" (e.g. tabular charges for reaching maximum range as designed without any modifications to the charge or projectile) rounds could be fired: for the 25-lb gun, it was 10,000 effective full charge (EFC) rounds. To put this in perspective, Soviet sources note that their powerful long range 2S5 152mm gun only had a life expectancy of 300 EFC rounds, and that the early T-72 125mm 2A46 gun had a life expectancy of only 200 EFC (e.g. sabot) rounds. Of course, firing reduced charges increases life expectancy and "super-charges" reduce it (e.g. each "super-charge" is rated at 4 EFC for life expectancy computations for the 25-lb gun). He notes that some guns were still fitted with their original barrels when placed out of service in the 1950s.

From my own memory, I thought I had read the 75mm L/70 & 88mm L/71 had service lives in the 400-500 round range. While the 75mm L/48 & 88mm L/56 lasted 3-4 times longer.

This is also part (yes just part) of the reasoning behind the US Army Ordnance Dept.'s decision to stick with the lower velocity 75mm main armament on the M4 series. They didn't want to be replacing tank barrels so often. Easier to replace the whole tank I guess.

[ww2steel]

Makes sense- that the long guns would wear out faster given the much higher stresses of pushing a similar sized projectile with at least 4x more powder out the barrel. Cool info.

Realistically though, with the exception of artillery guns I think any WW2 army would be being very optimistic if they thought that many standard issue tanks would last long enough to go through 500 rounds, even given practice shots.

I wonder, does anyone have info on how many rounds was a normal service life for a tank gun (before being toasted)? How often did armor actually require gunnery refits due to wear. (Not counting self propelled artillery.)

Mike

[JoMac]

All above points are good.

Also consider that the lower velocity 75 gun shells are a little smaller then the Higher velocity 75 shells, as there is less propellant needed. This gives a slightly higher rate of fire, and barrel life. The firer can see the lower velocity shells better, and thus make the appropriate corrections. Lower velocity shells may only need a near miss to damage or KO soft targets. This is because they tend to explode on the surface, where as the higher velocity will dig in the ground before going off.

[JoMac]

WW2Steel,

Basically you are right. There is no need to worry about that info as barrels would be simply replaced or changede out when the time arises. Among others, one important thing to remember is to simply try and put out as many, and or better tanks then the enemy, and hopefully it will help turn the tide in war.

[Redwolf]

The semi-short 75mm actually ended up on the Sherman because of (typical) U.S. mixing of services. The artillery somehow got a word in the tank design and demanded a gun that lasts IIRC 1500 shots. Otherwise they'd have a higher velocity gun on Shermans, but hey tank-fighting is for tank destroyers. The best part is that due to lack of German tanks to mess with many of the M10 tank destroyers with the shorter lived high velocity 76mm gun did indirect fire support. The Shermans on the other hand usually lasted firing just a couple rounds before they got kicked in the ass by the better German guns. Nice screwup.

Anyway.

Another advantage of the lower speed shells is that they reach into infantry fortifications better. Horizontal targets (aka ground level targets) are easier to hit (vertical ones more difficult).

The ammunition before firing is also smaller and you can load more HE rounds into a tank.

[Aco4bn187inf]

You have to ask how many HE shells the Sherman 75 got to fire at Axis positions before encountering the better German guns. Could be a considerable number on average, plus the Sherman was used as indirect fire at times (especially in Italy I think) and then there is the entire Pacific theatre, where the gun was probably fine for fighting Japanese targets.