Originally named Haddock until renamed while under construction, she participated in World War I as a patrol sub off the coast of the Azores in southwest Europe.

Upon completion of six months training, K-1 joined the 4th Division, Atlantic Torpedo Flotilla, Newport, Rhode Island, on 9 October 1914.

The techniques learned from these experiments were soon put into practice when U-boats began attacking Allied shipping bound for Europe.

K-1 departed New London, Connecticut, on 12 October 1917, arriving Ponta Delgada 15 days later to conduct patrol cruises off the Azores.

For the duration of the war, she conducted patrol cruises off the Azores and searched for the enemy U-boats, and protected shipping from surface attack.