"Presumably by "base of the tower" they mean base of the turret – some things get almost lost in translation."
Actually I think it is as mufh something that is lost in the current usage of the word by most modern English speakers, but is not lost by the etymology of the word in Russian. Or some such…
In most dictionaries the first definition you will find for the word "turret" is something like: "A small tower on a fortress or city wall, generally round in shape, that is used by defenders to fire in multiple directions." Or maybe a shorter version of that.
It derives from the old English / French word Touret, for small Tour (the French word for tower).
Again in most (but not all) English dictionaries it is only the second definition of the word turret that gets to something like "A rotating platform for a gun or weapons that can fire in multiple directions."
My understanding, subject to correction, is that Russian retains only a single word for Touret and Tour (turret and tower). So auto interpretation programs have difficulty determining the intended meaning as they translate.
So when reading translations of Russian language sources I use context to guide me, but almost always substitute "turret" whenever I see "tower" in the English version text.
In the OP case, the correct translation should be "… only when the shell hit the base of the turret, the tank was incapacitated." From that, you can proceed to interpret that it may have jammed the turret ring, or penetrated, or whatever you wish..
At least that would be my understanding.
-Mark
(aka: Mk 1)