In the original series from the 70s, there is no side mission to kidnap anyone. The original reason Domel did not outright destroy the Yamato was that he wanted to toy with them, so the torpedo planes were only sent to cripple the ship, much like the new series. Only now, it is to make a diversion, take out the Yamato's radar and allow for the infiltration team to get on board. In both series, the general end game is the same, have the drill detonate and then finish off the Yamato with heavy bombers.