Fire all to one battleship
i was in the same situation with my ix-B boat and i fired a first salvo of 6 torpedoes to the battleship and after some time with depth charges i was able to finish her with two more torpedoes.
if you fire 2 torpedoes to each ship probably donīt cause enough damage to slow down his speed and probably they could scape.
is better one bird in the hand than 100 flying :rotfl: