Under Pressure

HEAT is a much more complicated armour penetration mechanism than traditional kinetic penetrators, and thus leads to more interesting experiments. For example, in this one, the objective of the test was to determine how effective ERA was at disabling the heat blast, but more importantly, what an ERA block detonation would do to the crew.

The trials were performed on a model simulating a tank with ERA. Rabbits inside the model simulated crew.

Fig. 29. Overall view of model #2 with a U-5TS gun barrel installed.

Penetration, Part 8: Cold War Edition

Time passes, friends become enemies, enemies become friends, but the need to know what your enemies are capable of doesn't go anywhere. Naturally, as the USSR continued its research into weapons, the United States continued trying to discover information on those weapons. This is what they came up with.

PAM 30-60-1 Vol. 3 Pt. 1 (composite image from several pages)

Lots of good old friends, as well as newcomers, so let's go through this list and see what we can find.

The first gun is the D-56T mounted on the PT-76 amphibious tank. It seems new and exciting, but it's actually just a boring old ZiS-3 in a tank form factor. So boring and old, in fact, that the penetration data comes straight from this table right here, for APHE at least. The APCR data is not recorded in that table (probably because it has less penetration than AP at this range). HEAT is also new, and clearly a different round than was tested with the F-34. That one didn't perform nearly as well.

The next gun is the S-53, mounted on the T-34-85 and T-44. The rate of fire of only 3-4 RPM is rather low (average sustained RPM using all racks according to Soviet data is 6). The penetration for APHE is the same as the Soviet table again, but APCR is new, same as with the D-56T. Unlike the D-56, however, this round is actually more effective than AP at this range, which is probably why it doesn't get HEAT.

Next is the D-10T, from the T-54. Unlike with the predecessor, the rate of fire is straight out of the manual. Here, the penetration for AP is much greater than the old Soviet table (likely owing to post-war ammunition). The HEAT shell for this gun packs quite a punch, way above the dinky old D-56.

Now here's the good stuff, the smoothbore U-5TS from the T-62. The tank was built around the gun, and it shows. New APDS ammunition puts the D-10T to shame, and HEAT penetrated an impressive 450 mm of armour. 

The D-25 is next, installed on every Soviet production heavy tank from the IS-2 to the T-10. Penetration here is a little higher than the Soviet table (160 vs. 147). Otherwise, there really isn't that many new things to be learned about it.

The successor of this gun, on the other hand, is much more interesting. This is the "122 mm T-10 tank gun", or better known to most as the M-62, mounted on the T-10M, but compatible with any D-25 mount. The AP shell of this gun penetrated 185 mm of armour at 1000 meters, which isn't that impressive. The bigger improvement is the HEAT shell, which penetrates a whopping 460 mm.

The next gun is a little more obscure, the 57 mm Ch-51M from the ASU-57 airborne SPG. The values here are lifted straight out of the manual (although APCR penetration at this range is listed as 101 mm in the manual instead of the 100 in the table). Looks like American intelligence was doing its job properly.

The next gun has a fancy title, but this is just the plain old ZiS-3 again. Comparing data with the D-56 will give you some differences in the mount, but otherwise, it's functionally identical.

The D-5S-85 is another gun you should be familiar with, from the Soviet SU-85 SPG. The same gun was mounted on the more modern ASU-85. As expected, its performance is exactly the same as the S-53.

The D-25S is another "double", with all data identical to its tank-based version, but in the end of the list, the ML-20 awaits! However, it doesn't have anything new to tell us. Penetration data is, once again, pulled straight from the Soviet table.

HE vs. Armour

I've briefly explored the effect of high explosive ammunition on armour (disappointing American HE and much more exciting Soviet HE of various calibers), but nothing exceptionally scientific. However, a paper by V.V. Gayun, A.V. Grishkun, O.P. Gusev, and A.V. Lisin titled Investigation of Damage Dealt by High Exposive Fragmentation Shells to Armour published in the Armoured Journal (Bronetankoviy Vestnik) gives some glimpse into how shells of various calibers act against armour. In the interest of brevity and not getting bogged down in scientific jargon, I will only translate a portion of the article and provide some figures.

Thankfully, there is plenty of practical data to go off here, and not just theory. The experiments involved 152 mm shells, whose devastating effects we have already seen, as well as Soviet 100 mm, 115 mm, 125 mm, and 130 mm shells. Of course, only knowing where you stand is of limited use if you cannot compare your progress with that of the potential enemy, so the British 120 mm gun with its HESH shells also makes and appearance. These shells are fired at armoured plates 2700 by 2500 by 170 mm, with sensors behind them to measure the impulse, which is judged by the scientists to be proportional to the damage caused inside the tank to its crew and equipment.

Since we've seen what a 152 mm HE shell can do, let's take a look at experimental data for this caliber first. Players of World of Tanks will be used to HE doing the same amount of damage to the tank no matter at what speed its hits, but in reality, this is not the case:

"An analysis of natural shots, static detonations, and calculations shows that the contribution of the explosive filler of a 100-152 mm HE shell contributes around 5-10% of the overall impulse (at an impact velocity of more than 700 m/s), and the main damage to the armour plate is dealt by the impact of fragments.
...
When increasing the impact velocity starting from 600 m/s, the impulse of a 152 mm HE shell grows considerably, and when decreasing it from 400 m/s to 250 m/s, it decreases by 2-4 times. When the impact velocity is 950 m/s, the impulse is 50 and 40 kNs for 0 degrees and 60 degrees respectively, which is 2-2.5 times greater than the 125 mm OF-19 shell.

At angles of impact close to zero, and the velocity of 250 m/s, the impulse of a 152 mm HE shell is less than that of a 100 mm HE shell with the velocity of 900 m/s. When the angle of the target is increased from 0 to 60 degrees, the impulse of shells hitting it at 850+ m/s decreases, but the impulse of shells hitting it at 250-700 m/s increases. Therefore, the 152 mm HE shell has a higher effect against armour than a 100-130 mm HE shell at impact velocities greater than 650 m/s and a comparable effect at lower velocities."

Fig 1. Experimental dependence of the impulse of 152 mm HE shells on the impact velocity (vc) at several angles of impact (α).

The ML-20. whose devastating effects on armour we've already seen. is not a very high velocity gun. Shells hitting the enemy would be flying at less than 600 m/s, giving us a pretty small range of impulse that causes such damage. How does this compare to other HE shells in the Soviet arsenal?

Fig. 2. Experimental dependence on impact angle α of the impulse from HE shells on an armoured plate.

1. 152 mm HE shell (vc = 950 m/s)

2. 130 mm HE shell (vc = 910 m/s)

3. 125 mm HE shell (vc = 780 m/s)

4. 115 mm HE shell (vc = 850 m/s)

5. 100 mm HE shell (vc = 790 m/s)

The 130 and 152 mm heavy artillery is the undisputed king here, but at very high velocities. Corps level artillery and tank guns would be unable to fire shells so fast. 100-125 mm tank guns (the D-10T and its post-war smoothbore cousins) seem like they woudn't do as much damage as we've seen the ML-20 dish out, but comparing the impulse values of these guns to the values in fig. 1 says otherwise. These guns achieve an impulse of about 20 kNs, same as the ML-20.

Now, let's see how these guns compare to British HESH. Unlike traditional HE, the explosive filler spreads itself around the plate it impacts to increase the effect. How much does this increase the effect? Here is the impulse achieved when hitting "a tank" (the specific type of tank is not mentioned).

Caliber, mm	Type	Impact velocity, m/s	Impulse, kNs
Turret
115	OF-18	680	8
125	OF-19	850	11
120	HESH	620	12.5
152	OF-29	800	15
Hull roof
115	OF-18	800	8
125	OF-19	850	9
152	OF-29	800	19
Upper front hull plate
115	OF-18	860	11
125	OF-19	850	14
120	HESH	620	12
152	OF-29	800	28

Turns out, not much better. 120 mm HESH is comparable to the slightly faster flying 125 mm HE, and it still greatly surpassed by 152 mm HE.