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Sectional density in very rough terms pretty much refers to the projectile's ability to penetrate a certain object at a certain speed. The higher the SD the higher the penetrative ability pr. amount of speed.
I was kicking it around in my head last night and realized the 12.8cm gun was the same size but longer than the US Navy's 5" 38 that was used on US destoyers as a primary weapon during the war. Round weights about the same. 50Lb or so.
At that point, the penetration of the round is impressive but so is the explosive effect. One of those things go off against the side of a tank will probably disable if not destroy it.
Honkin' big round.
In 1949 a Churchill with 235mm of applique armour was fired at from 100yds by a German 128mmm gun.
2 AP hits on the hull left gouges and cracks but did not penetrate. One hit on the turret knocked it off but did not penetrate. 2 rabbits placed in cages inside the tank survived and showed no ill effects!
I agree, the picture's cool. But I have to also mention...rabbits...the physical make-up of a rabbit is ...well, a lot different from that of a human. Given the size of a human in such a confined space, I'm thinking physical damage would have been more likely especially if the freakin' turret fell off.