Good set of rules, and I like the card-back coding system. I’ve provided a few suggestions below, if case they’re of any interest.
Powerful Torpedoes No of cards: 3 - Japan & Germany starts with one card each
Comment: “Powerful Torpedoes” is a little vague, so given that the advantage is limited to Japan and Germany, how about changing this to either Oxygen-Fueled Torpedoes (a technology which Japan might have shared with Germany) or Acoustic Torpedoes (a technology which Gremany might have shared with Japan)?
Human Wave Attack No of cards: 4
Comment: Technically this should only apply to Japan, since no other country (except perhaps arguably the USSR) used such tactics.
Underground Factory No of cards: 3
Comment: With the exception of the Mittelwerk slave-labour complex, I can’t think of any examples of large-scale underground factories. “Camouflaged Factories” would be a better alternative: concealing an existing factory can be done much more cheaply than building a new one underground; the technique was actually used in WWII (notably in California, where the roofs of factory buildings were camouflaged to look innocuous from the air); and it would explain the reduced damage on the grounds that some of the bombs would have been improperly aimed.
Flying Ace No of cards: 4
Choose a friendly fighter during conduct combat phase that scores a miss and change it to a hit.
Comment: I think the phrase “Fighter Ace” is more commonly used and more precise.