I thought this was going to be about a hybrid submarine/aircraft (das Boot)...
Here's what we used to wear in V-Force in the '70s, and I think we also wore this pattern boot during RN helo flying training in 1969/70 (along with Mk1/G cloth inner helmet combo. I don't recall when exactly we changed over to the streamlined versions (but some of the more...traditional, let's say...kept on wearing these ubtil they were forcibly taken from them).
The upper portion could be cut off, leaving a shoe-like remnant, which would fool any Sov bloc citizens if you were attemting E & E...yeah, right...
Mister B