What was the purpose of this, someone challenged the tank to a cannon ball challenge?
I wish I had a solid source on this. The best I can find is a 6-year-old Reddit comment:
This particular jump with the BT-7 cavalry tank was performed by a tank test pilot Evgeniy Kulchitsky, he mentions in his memoirs that it was a very challenging test to perform (15m height, 42m length of the jump), requiring challenging practice and long preparation. You had to adjust the rotational speed of the tracks mid-air to not outright lose them, assume a (relatively) safe position and then continue to pilot the tank after landing to get it to the shore.
The reason for this testing was to make sure that similar jumps were a viable tactical option (fording rivers at speed, for example) and that both the crew and the tank could manage it and remain effective.
Holy crap there was someone inside that thing? How was their spine not destroyed on impact?