1 Jamie: It's rather cramped in here.
1 Adam: It's a submarine. What did you expect?
2 Jamie: Hang on, this sonar screen is indicating a blip.
3 Adam: It's the monster!!
4 Jamie: {external view of sub} But we're not even in the loch.
4 Scottish mining engineer: Wha' manner o' unholy contraption is this??

It's so cramped in there that there isn't even room for seats.

Although sonar is mostly used in water, it can work in air as well. There it's essentially the same thing as the echolocation used by bats, as well as oilbirds, shrews, and a handful of other non-marine animals^[1]. Even humans can learn to do it!

[1] Marine animals like dolphins and other toothed whales use sonar too, but underwater, not in air.