It's been a while since I read a book about the Battle of the Atlantic and I won't have time to re-read them, so these suggestions might be flawed.

Regarding broadcasting and tactics, the hard part in fighting convoys is finding them in the first place. We should place a line of around 4-8 submarines patrolling a north to south course along suspected convoy routes gained from intelligence. When a submarine detects a convoy, it is to send information about the size, speed and bearing of the convoy to the BdU, where we can coordinate our subs on intercepting courses. If the convoy is spotted during the daytime, the submarine is to shadow the convoy informing the BdU of changes in the bearing and speed until the fall of the night, when she is free to strike. During the night, they are free to attack at will after reporting the information about the convoy.

Regarding ASW equipment, the main means of detection for the Brits are Asdic (Sonar), short-range radar, aerial spotting and the fact that they have cracked Enigma. Regarding means of destroying submarines, you mostly had depth charges at this point.

Anyway we could suggest adding an extra rotor to change the Enigma code, although historically that did not occur until a while later.

Regarding the positioning of our U-boats, I would suggest concentrating on the Mid-Atlantic gap.