Tuesday 28 July 2020

Warspot Article: Firefly Development

The British developed a first class anti-tank gun during WWII, but had no luck with a platform to put it on. The solution came from abroad. Although it took a lot of effort, Sherman tanks proved capable of mounting this powerful gun. Read about the trials of the Sherman Ic and Vc tanks in my latest article on Warspot.net.


  1. The diagram showing the penetration chances of the 17-pdr versus the Tiger I and Panther, with different ammunition types--how was the armor resistance of these tanks determined? Are we talking about upper glacis, turret, or some amalgam of averaged armor protection for overall resistance?

    I was somewhat surprised the 17-pdr APCBC round was deemed by the British to struggle so against the Panther's front. I would have thought it needed to be close (~ 500 meters), but that diagram suggests at even point blank range the chances were not good.

    1. Diagram probably show upper part of hull. I must add that in my opinion that's not strange that even 17 pdr can be to weak gun for penetration Panther glacis- angled armour can protect far better that it's LOS (Line Of Sight) suggest. Also according WWII charts Panther glacis protect from 17 pdr shots. And most important argument- Isigny test: https://wargaming.info/1998/us-army-1944-firing-test-no3/#.WKobrvJF57E

      Allied WWII charts: https://milimoto.wordpress.com/2019/02/16/alianckie-armaty-kontra-pantera-i-tygrys/

    2. I was supposing the Panther's glacis to have a theoretical protection of ~170 mm, and the APCBC round for the 17 pounder at 500 m in the tables I've looked at ranges from 175-163 mm, depending on armor type. Then one might consider the effects of 'variable' German armor quality. I was expecting the Panther's armor to offer good protection, but not great protection.

      It's also odd, as by the same tables I'm looking at the limit turret penetration by the 17 pounder in the WWII charts (the 2nd link you gave) is way too optimistic; shooting at rounded surfaces is always a crap shoot; just comparing it to the limit given for the US 3-inch gun on the same page it seems to be only a little more than the raw armor thickness of the Panther's 100 mm mantlet as flat armor, which isn't realistic. That's the best-case scenario, and not a typical one.

      It's also that in most of the tank books I've read, the 17-pounder gets all this high praise, as in "the British had a solution to Tigers and Panthers with the Sherman Firefly" and maybe that's true for the Tiger I (in diminishing numbers in 1944) but it's not worlds better than the US 76 mm against the front of a Panther.

    3. IIRC, according "WWII Ballistics, Armour and Gunnery", Panther tank glacis protect better than 200 mm thick vertical plate versus 76 mm gun (site 92).

    4. Hmm, AKMS.

      The Panther had ́80 mm of plate sloped at 55 degrees. By the "US Army criteria" I have seen, that represents a slope multiplier of either 2.1 or 2.13. That is what I used.

      I have a table showing other slope multipliers for the same angle:

      A) 2.20 (for Ni steel; wrought iron, or WWII homogenous plate)
      B) 2.35 (Homogeneous Cr-Ni/Cr-Ni-Mo Naval armor)
      C) 2.05 (Face-hardened steel armor; it also lists "KC, KNC, Harvey(?) which I do not understand).

      None of these get the Panther's armor to 200 mm. Nor does 200 mm 'make sense' against other weaponry that we know could penetrate. If you take the D-10, for instance, and if you trust the Livingston-Bird calculations to adjust Soviet penetration figures to the US/British standard, the D-10 can penetrate 164 mm of armor at 1000 meters and 144 mm at 1500 meter (BR-412 shell), while the Panther has 80 mm at a slope modifier of 2.1. Adjust the slope factor downwards for overmatching, and the Panther's armor resistance to the BR-412 calculates to be 148-150 mm, depending on rounding error. That means the D-10 should be able to penetrate a Panther's glacis at 1000 meters and should fail at 1500 meters.

      That's exactly what Soviet testing found:


    5. Citation from book, from 92 site: "The Isigny Panther glacis plate had measured angles from vertical of 57.6°, 57.1° and 56.9° due to ground slope. Assuming 85mm plate thickness, 0° equivalent resistance of good quality Isigny glacis armor would equal 248mm, 240mm and 236mm against 76mm hits, which would defeat 17 pounder hits despite reductions in armor quality from medium or high severity flaws.

      Against Panther glacis with medium flaws and 85mm plate a 55°, armor resistance would still exceed 17 pounder penetration at all ranges (212mm vertical equivalent resistance after 0.95 flaws multiplier".

    6. Small correction: "Against Panther glacis with medium flaws and 85mm plate a 55°, armor resistance would still exceed 17 pounder APCBC penetration at all ranges (212mm vertical equivalent resistance after 0.95 flaws multiplier)".

    7. AKMS,

      That's a more generous slope factor than for US naval armor for that angle, 2.9 to 2.78, and I don't see why the Panther would have that. Nor would the D-10 have penetrated the Panther's front, which it most certainly could, the ranges it did. The slope factors Bird and Livingston cite would predict the D-10 would struggle against the Panther's glacis, even at point blank range, even after adjustments for overmatching and for poorer armor quality, and yet the D-10 penetrated in Soviet testing by well over 1000 meters.

      So, no, I don't believe that report's calculations. At least they don't mesh in the larger picture of things.

      I have a copy of Livingston and Bird too, and I get frustrated reading it. There's a lot there that's good and illustrative, but insofar as translating foreign AT test results to the "British/American standard" by hook and crook when you *HAVE* data on those same weapons that *were performed* by the British and Americans, and your translations do not agree with those results, is just strange. Plus I have seen a factor they put into they put into make their calculations on German weapons, and Soviet weapons, which I think are just plain wrong or at least suspect.

  2. Calculated protection basis is one thing. I like to look at test results. In the Panther shot to pieces test the upper front hull seems to be penetrated at 900 yards. The APCBC round would penetrate 153mm at that distance.

    1. Both calculations and test results are useful. Calculations are a 'theoretical' artificial, but so are tests done on metal plates. My understanding is that one of the reasons why the Americans were not terribly concerned about the Panther was that their own testing on their own domestic armor showed that their 3-inch and 76 mm guns should have no problem penetrating its armor, but their tests were not a good model because the composition of their domestic armor used in testing wasn't a good analogue for German armor.

      We're talking about a phenomenon that intrinsically contains a high degree of variability, you need at least dozens if not hundreds of shots to pin down a good average value, and it's almost impossible to get enough captured enemy armor in non-compromised condition for such tests. Shoot at any single tank enough, and you'll get penetrations because of the armor being weakened (that's actually realistic--that's the first thing that I thought of when I saw this post:


      ...was "that Tiger II may have been hit near that point by something else previously, which is why there was a penetration").

      Ditto with captured enemy guns. You have to either also capture a fair amount of ammo with these to do a proper test.

      So what do you do? I'd be actually curious to know. What I'd think is that with a captured gun, you'd either a) have ammunition for it specially made for the test (definitely a 'rich man's solution') or you'd perform the test with the ammo you'd captured at one "can't miss" range (as you can't afford to squander ammo with misses). Then when you had a good value for penetration at that specific range, knowing the shell weight, caliber, and muzzle velocity of the captured gun, you could use the DeMarre equation to calculate the penetration at other ranges.