Managed to put some weps on the hog islanders myself, but a version from people who know what they're doing is certainly better
Re the convoys, i ran into one last night, consisting of an aux gunboat, a old destroyer, a large modern and a large old, a medium tanker and two modern troop transports.
Daylight periscope attack, 3 Mk18s on the leading gunboat, apparently got speed wrong, one Mk18 clipped the stern and disabled the gunboat.
Shot two Mk18s from the stern tubes at a troop transport and sank it, destroyer came charging, shot 3 Mk23s at the DD but missed. Suddenly I heard "bang" and "she's going down"! One of my torps had randomly smacked into the other troop transport and sank it!
Made another submerged attack on the crippled gunboat and sank it.
Made a night surface attack on the rest of the bunch, firing two each at all surviving three merchants. Hit all three, the tanker with one (stayed afloat), the old large with two (went down) and the modern large with one (stayed afloat).
Made another run on the modern one with stern tubes and sank it.
The destroyer was mysteriously stopped, but accelerated out of the way of my last fish (a real steam driven ship could've never done this!)
Then I had no torps left and with the RFB gun reloading time I couldn't finish off the crippled tanker before the destroyer showed up, so I had to leave two survivors....