Monday 6 March 2023

Video: IS-2 vs Panther, Math and Reality

I've frequently seen the claim that the front of the Panther tank was nearly invulnerable to the IS-2's 122 mm D-25T gun if correctly angled. Indeed, penetration equations suggest that would be the case, but reality is a lot more complicated than that. In this video I go into detail about how line-of-sight armour thickness doesn't tell the whole story.


  1. Hi Peter. I replied on your Youtube Channel, but I have looked into this a bit more.

    I have the Aberdeen penetration curves for the A-19, which is essentially ballistically similar to the D25-T, firing the BR471B round at various angles of impact. While I can't find the 'chart paper' graph I have anymore on the web, I have found this that seems to be constructed from the same data:

    If you calculate that overmatching by the 122 mm round hitting 80 mm armor reduces the effective armor of the Panther's front hull (80 mm @ 55 degrees slope) down from 145 mm (just the cosine value of 55 degrees ) or 168 mm (US Army calculation for 55 degree slope) down to about ~125 mm effective armor:

    1) It still predicts a penetration at of the Panther's hull at 0 (horizontal) degrees out past 2000 meters (the chart paper graph copy I have appears to be 2300 meters, while the graph I linked seems to be c. 2100 meters);

    2) Angling the Panther at a 30 degree (horizontal) slope graph predicts a penetration of the same front hull at 1500 meters (1600 meters for the chart paper graph). Less, but by no means down to '100 meters'.

    These are for the BR-471B capped round. The BR-471 uncapped round I'd presume to do worse, but not much worse as both these curves seem to predict both Soviet test results and combat results pretty well.

    1. BTW, the British data for the same A-19 BR-471 round is here, and concludes that the Panther's hull armor will fail with a higher degree of certainty:

      This graph at both 0 degrees and angled at 30 degrees has the Panther's hull armor failing out to 3000 (!!) meters.

  2. Well, Peter. My second post also disappeared. Here goes again.

    As I wrote on the Youtube channel, I think the D25-T's ability to penetrate the Panther's front hull, be it angled horizontally or not, does not correspond to any special case of violation of the theory of a round penetrating armor, once overmatching is considered.

    Here is a chart which I think comes from the Aberdeen data for the BR-471B round at various angles:

    I have the original Aberdeen data on image of the chart paper, but can no longer find this online anywhere. If you calculate that the Panther's upper hull will be reduced from c. 170 mm effective armor (US Army slope factor) or from 145 mm (cosine calculation) to about 125 mm effective thickness by overmatching, from the chart above, you see that the D25-T can penetrate the Panther's hull at 2100 meters at 0 degrees, and can still do so at 1500 meters if angled at 30 degress. The original graph on chart paper seems to indicate armor failure at longer ranges, 2300 meters and 1600 meters, respectively.

    You can also do this the British data on the D25-T:

    The British data is even worse for the Panther, as it predicts failures in both 0 and 30 degrees out to 3000 meters!

    Now, all this data is for the BR-471B round, not the uncapped BR-471 round, so this data may not be as favorable. But by tests you have posted on penetration testing of IS-3 hulls the sharp-pointed BR-471 round didn't do that badly against the IS-3's front, which is nothing if not sloped.

    There are various ways to calculate the effects of overmatching too. But none of them would indicate insofar as I can see that the penetration threshold would fall from 2000 meters-plus down to 100 meters simply by angling at 30 degrees.