Commissioned on 1 September 1938 under the command of Oberleutnant zur See Hans Bartels, she was used to transfer the Marinestosstruppkompanie to the battleship Schleswig-Holstein on 24 August 1939 in preparation for the Invasion of Poland.

In February 1940, M-1 sank four Esbjerg fish trawlers, Ejjam (E 92), Gerlis (E 456), Merkator (348), and Polaris (E 504), killing all 16 crew members.

Bartels later justified his decision with military necessity, as the neutral fishermen allegedly send coded messages to alert British forces to his presence on the Doggerbank.

After the German attack on the Soviet Union, M-1 was part of the naval component of Operation Siegfried, the occupation of the islands Dagö, Ösel, and Moon.

On 12 January 1945, M-1 was sunk in Nordbyfjord, near Bergen in Norway, by Avro Lancaster aircraft of 9 and 617 Squadrons, Royal Air Force, using Tallboy bombs.