spice it up with a just launched torpedo with a short "bubble trail" from an open torpedo tube and maybe a faint trail from the sub's prop(s) and a second (Fire 2!) torpedo just partially emerging from a second tube. A WW II sub with bridge, deck, railings, assault and defense guns, etc. would be more interesting than a modern cigar tube sub, imo. The surface might include a snorkel as well if the back story included the sub being surprised by an opportunity during running submerged on diesels and charging the batteries. Just some random thoughts.