There have been various attempts over the years to use “combined forces” as a house rule or patch, but the problem arises that you are essentially letting certain pieces move or fight twice in one full turn if they are allowed to stage up on UK turn then attack again during US turn (or vice versa) once they are in place.
You can already exploit this to give fighters 2 extra moves, by putting US fighters on a UK carrier, moving the UK carrier, then the fighters are staged 2 spaces further than they ever could have flown, not to mention that they are only capable of crossing the north atlantic if there is a carrier there to catch them. The only problem is that if the fighters fly off or die during the US turn, the UK could not sub out or replace the empty carrier capacity without an intervening Axis turn, leaving empty carriers vulnerable.
The fact that UK and US cannot fight together makes KGF very difficult. You have to guard 2 or 3 SZs to stage your stuff, any one of which can be subject to a full Germany attack. Then, once you attack Denmark and stack it up, the fleets still have to face defensive scrambles UK alone or US alone. When you move in for the kill, you also have to guard a team in SZ 112, and Germany will hit the weakest fleet, the one crossing if not the one invading.
losing one allied fleet before its troops are delivered during a KGF is a loss. So, this requires that each of US and UK be independently able to fend off a German strike–you cant rely on the US to provide the carriers and capital ships and let UK focus on only transports, for example.
The only upsides to the no combined forces rule is that you can:
- use the team that moves first to smash through blockers
- use the team that moves second to land fighters or men stax in defense of a recently-captured territory; this is the only way to hold German territory