This is an interesting thread. There’s a lot of insight from long time players that making points that I wouldn’t think of until it was tried a few times.
After reading Clay Blair’s exhaustive 2 volume work on U-boats (basically every single recorded sortie during the entire war) it’s clear that Allied transports were well protected. The USN’s primary goal was no troopships would be lost and with the exception of a single loss in the Med, they completed that goal. They were so concerned with that loss, it was never disclosed until well after the war.
Japan on the other hand, not so much. Troopships were expendable and torpedoed at will by US subs, although tragically with prisoners aboard.
In my mind it really should be up to the side to protect. That said, nothing cheeses me more than an lone bomber flying long distances and wiping out a group of transports with impunity. Strategic bombers were horribly inaccurate against ships, especially small ones.
Transports did have AA capabilities, early in war armed freighters were open season to U-boats, as opposed to others that were required to be boarded and evacuated before sinking. Armed transports were also effective against U-boats since conning towers were easily penetrated, plus ramming. Freighters were often disguised with enclosures that hid guns that opened fire when the U-boat closed to use their 88 (torpedoes were very expensive and unreliable).
My son and I are going to try a compromise:
Unprotected transports-
Can defend against aircraft and subs on 1.
Cannot defend if any other surface ship is present.
Sub(s) v unprotected transport(s): sub attack value increases to 3, the transport(s) roll one defense die per exchange, regardless of number ships, otherwise the battle progresses normally, i.e. until resolved or broken off. Reflects the ease that U-boats dealt with stragglers.
Plane(s) v unprotected transport(s): each air unit can battle one transport only. If there are two AC and five unprotected transports, only two can be engaged during that turn. Torpedo and dive bombers carried one ship-sinking ordinance and usually had very limited time over targets. The transports would be scattering and evading, a squadron of aircraft wouldn’t be able to stay on the scene to sink 6 groups of transports.