If you're an aide in Washington, you bathe twice a day. If you're fighting across a Pacific island, maybe once a week. North Africa, when you can get water to spare. A bit better in Europe.

What "element of surprise"? This wasn't a series of ambushes. It was a war with artillery barrages announcing the probability of attacks later today.

I recall a cartoon by Malden of a returned vet asking his wife, "What's wrong with that shirt? I've only worn it a week!"

Men bathed whenever they could, but we're talking, say, November in Europe. In the Pacific, once a beach was secured, swimming did for bathing if you could rotate back there. There's plenty of pictures of GIs hitting the rivers when they could.

Old Sarge discusses that if you can only do your teeth once a day, do them before bed, and how to get a little clean to prevent skin problems.

Sources:

How to Keep House in a Foxhole USA pub from WW2

How to Get Along in the Army, by "Old Sarge"