Read the book 'Conflict over the Bay' by Norman Franks, which covers RAF Coastal Commands hunt for Uboats during May-August 1943.
This is the critical time period where tactics on both sides were evolving wrt to UBoat-vs-Aircraft.
Essentially the Allies developed 'search blocks' in the Biscay Bay, where many aircraft would patrol. This area was wide enough so that a UBoat would not be able to cross it without surfacing to recharge batteries, thus a better chance of being detected by ASW - Aircraft as well as Hunter Killer groups.
Every one of Donitz's fight it out tactics brought only limited success and was quickly nullified by a change in allied tactics.
- If a single UBoat tried to fight on the surface, a single aircraft would attack. Invariably it meant a damaged or sunken UBoat. A damaged Uboat would have to return to port.
Allied aircraft usually carried only enough 'DCs' for one attack (sometimes they would use half their ordinance for a second attack to foil the Kaleun).
If the Uboat did not sink, if the aircraft wasn't badly damaged, it would circle the sub until other aircraft, hunter killer groups arrived, or had to leave for shortage of fuel.
- Eventually Donitz ordered 3 Uboat formations to transverse the search blocks on the surface.
What the allies did when discovering this, was to circle the sub group calling in more aircraft and HK groups. Up to five aircraft would be circling the 3 boats like vultures waiting to pounce.
Communication between aircraft, and between subs did not exist so neither in each group knew what the other was up to until they did something. Also keeping subs in formation while watching the vultures was a big problem and usually one sub went out of formation - the aircraft would nearly crash into each other descending on this unforunate sub.
With the ensuing chaos, the other subs would then try to submerge - very few got away unscathed.
If not enough a/c coulld be called in, a HK group could arrive within a few hours... and the Kaleuns definitely didn't want this. Some subs got away only to be hammered by HK groups that were guided in by the aircraft.
I'm not sure whether SH3 takes all these factors into account but one can confidently say that you should crash dive.. even for a seagull
