So I realised that testing took place with default loadouts.
Changing an earlier P-39 variants default loadout which I think is 20mm cannons may be beneficial.
What is needed is a Ships_small class where vessels below a certain tonnage such as destroyers, corvettes, trawlers, barges and landing craft can be attacked with smaller calibre guns.
What we don't want to happen though is the same problem faced on land, dive bombers dropping their ordinance then endlessly strafing till they run out of ammo or get hit.
Now faced with a greater idea of what's occurring, I will test aircraft with logical weapons.
In terms of manoeuvre task, I notice they strafe as though they're attacking a vehicle column.
Always from the rear of the ship, is there another manoeuvre that would make them attack from the side which is more realistic?
EDIT: Add P-39D2 and Hawker Hurricane Mk. IV both with changed default loadouts.