We use the army pieces from the 2008 RISK as movement trackers.
I have seen a lot of people use the cities from this game as Industrial complexes and such.
The army pieces are arrows with either 1 chevron or 3 chevrons. So when we move something we place the corresponding arrow piece. Once all the units movement points are spent we flip the arrow upside down.
The USA cannot move any units into any land territory that’s not their own until they are at war.
So, no, they cannot send fighters to the UK until they are at war with Germany.