one thing i might point out is that in shallow water most large ships dont actually sink as they would in deeper water they just flood til the settle on the bottom and dont count as destroyed (which makes sense if you think about it all the tommys have to do is patch the holes and pump out the water)
when i raid harbors i go for broke just hammer every ship with 2 or even 3 fish to ensure a kill either by simply running it out of hitpoints or dealing critical hits
which usually means limiting your targets to 2 or 3 ships or finding a secluded corner to reload your tubes
oh and some targets i heartily recommned
new york harbor(minmal defenses in 1941, rich with targets)
gibralter (best raided early war before sonar gets mean, usually lots of big warships here)
freetown (big juicy targets usually)
rejayvik (lots of big warships usually, weather can be uncooperative this far north however)
good luck all you wannabe Priens
