Well here’s the way I look it… Assuming a J1 DoW (fairly likely if the Axis player is going for the jugular) then a USA max bomber buy, is basically the only purchase that can forestall Sea Lion, or at least push it out another round (since bombers are 1 move E.US to London). But even if J2 DoW, the bombers can still be launched with a massive stack attack hitting on a 4, with the magnified build (e.g. almost all money dedicated to this one unit type) and as much fodder to launch on a key defense if necessary. And since Russia’s defense seems to be linked so integrally to UK fighter support, I don’t see why anyone would pursue a “Russian” defense strategy that allows any chance for London to be captured.
The cheapest fully stacked transport combo cost 13 ipcs (2 inf), the strategic bomber costs 12 ipcs. Transports take 2 rounds to put into position on London and require a defensive fleet to escort them. Several more rounds to drop anywhere to support Russia directly. The USA Bomber armada takes one move to London and then one move into the Med or to anywhere on the eastern front that they might be needed for critical defense once G DoW. The transports can’t threaten warships or bomb factories/bases while they move out, whereas the strategic bombers can. So for me, its hard to see the argument for buying anything but Strategic bombers with USA in the first round.
How does this relate to Russian defense doctrine? Because the Russians have no control over when they get to join the fight in Europe. The UK has no way to control what the Germans might build/do in their opening round. So in either case, you can’t really depend on those too nations being able to do anything specific. Japan has a much stronger incentive to DoW early though, which means that USA can potentially swing the outcome on the Eastern Front, if they are ready from the first round with a bomber armada that can reach Russia within 2 rounds.
If you prevent the Sea Lion option altogether or make it prohibitively expensive on G, then you force a redirection on the eastern front, where at least you will know what to expect coming at Moscow. If Sea Lion, then the game is likely a gamble regardless, Germany throwing caution to the wind haha, but if G crushes East on the Center (most likely Axis plan anyway), then Allied control of the Center is basically a game of speed.
Bombers have the most reach, which means they are the ‘fastest’ US unit on the board, the first that can get to the Center, even if just being used as fodder pips hitting at a 1.
Everything else you might do with them seems to be supporting Russia indirectly, by pressuring G/I (via the Med crush for example), but even there, a Bomber armada can make any transports that are on the board more powerful by a pretty substantial order of magnitude. Bombers give you the quick option to redirect as well, and actually defend a key territory if necessary. Whether London or Egypt or on the Eastern Front to secure the Russian lines, and they can get there, basically as soon as USA is at war.
So for me the Russian defense doctrine is basically, “step one: buy a bunch of bombers with USA! step two: Things that Russia should do…” haha ;)