Love it! Also am heinously bad! Need help. :)

[Skubber]

Getting all the ships in the tutorial is quite hard, I think.
Lots of good advice given in this thread so far.
Basically if you can hit the target from the side, close to 90-degrees, set the torpedo triggger for "I" (impact). Even then the torpedo has to be set not to deep, or it will glance off the angle of the keel. It will take some practice to find the depth setting you like.

At any other angle (but also including 90-degrees) you want to set the topredo trigger for "M" (magnetic). For this to work, the torpedo has to run under the target's keel. Early in the war, this mechanism was known to fail fairly often, so much so that Admiral Donitz banned its use for a while.

Later in the war, though, this is the preferred setting, becuase you can take out a ship with 1 eel running under the middle of the boat.

Even knowing all this ... I had to play the game for some time before going back and trying to "win" the tutorial. I plannned my strategy for taking all the ships beforehand. Got them all eventually, but I still missed that pesky merchant with my first eel, even knowing beforehand what he was going to do!