Wisdom of a WWII veteran:

"If you encounter a unit you can't identify, fire one round over their heads so it won't hit anyone.

If the response is a fusillade of rapid, precise rifle fire, they're british.
If the response is a ♥♥♥♥♥♥♥♥♥ of machine-gun fire, they're german.

If they throw down their arms and surrender, they're italian.

And if nothing happens for five minutes and then your position is obliterated by support atillery or an airstrike, they're american."