The T was never for Tank.
It wasn't a tank gun, and it wasn't an anti tank gun. Somebody uninformed saw how big it was and made the connection that it was as big as a tank's gun (must remember the time frame, some tanks at the time still had quite small guns compared to end-war stuff).
It's an oft-repeated but debunked story that keeps popping up, so please don't feel offended that I had to correct it.
The Yak-9D was the long range version, if I recall.