U-boat was short for "Untersee", the German word for
"Undersea"
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It is a submarine. Spelled U-boat from the German Untersee (under the sea)
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90 Degrees East Ablation Lake Lake Bonney Lake Chad Don Juan
Pond Lake Ellsworth Lake Fryxell Lake Glubokoye Lake Hoare Island
Lake Lake Jabs Jackson Pond Lake Lagernoye Lake O-ike
Prilednikovoye Lake Princeton Tarn Lake Profound Sea Lion Tarn
Simmons Lake Sovetskaya Lake Untersee Lake Vanda Lake Vida Lake
Vostok Yale Tarn Zapadnoye Lake Zub Lake Lake Zvezda
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I think you are referring to U-boats which is are
submarines.
U-boat means untersee boten (undersea boat). They were German
vessels.