Nice story and pics. It may sound strange, but part of the fun of submarine sims is experiencing disappointments like this. You always think back on the "one that got away".
Whenever I play Trigger Maru I'm obsessively careful with the periscope - only using it to take quick peeks. Very impressive you scored six hits after being spotted - when that happens to me I usually have to break off the attack.
It's surprising that the BB survived - you'd think that six torpedoes would open up enough hull compartments to overwhelm damage control. Even taking into account the lower explosive power of Mk 18's. Better luck next time!