In addition to what sawjet mentioned with wire guided torpedos, I think they might also have hoped for the nuclear warhead the VA-111s originally had to destroy

In addition to what sawjet mentioned with wire guided torpedos, I think they might also have hoped for the nuclear warhead the VA-111s originally had to destroy the incoming torpedo. By being particularly fast, the supercavitating torpedo may have intercepted the enemy torpedo soon enough for that to work.. maybe.