To me it’s not a bad move if you only send the transports. The Germans will destroy them but you now have US ground units in the race for Africa.
That’s usually the way I play it. Especially if Germany is successful in Egypt. And like Hobbes said, if Germany decides to go after the US troops you’ve taken a turn away from it’s attack on Russia or the UK Navy.
Besides, it’s about the only thing the U.S. can do turn one. I’ve been teaching a couple guys how to play and it’s tough to tell the US players, who has waited almost an hour for his turn, to just make some buys with a plane movement thrown in there and wait another hour before it can do anything else (and there might not be much turn two either).