When was the U-boat introduced?

Answer 1

Germany's first U-Boat, number U-1, descended from a batch of newly constructed submarines for Russia during the Russo-Japanese War of 1904-1905. Russia received four or five submarines, and Germany commissioned it's first U-Boat in 1906.

Answer 2

The first German U-Boat, U1 was taken from a batch of Karp class subs being sold to Russia during the Russo-Japanese War in 1904. The U1 was launched into the German Navy in 1906.

Answer 3

1942