Type: II-D
Built by: Deutsche Werke (Kiel)
Launched: 18 May, 1940
Commissioned: 27 June, 1940
Feldpost Nr.: M02840
Sunk: 18 June, 1941
Sunk by: HMS FAULKNOR, HMS FEARLESS, HMS FORESTER, HMS FORESIGHT, HMS FOXHOUND (all destroyers)
Location sunk: 100 miles W of Cape Trafalgar
Position sunk: 36.04N x 07.29W (2 men lost)

Skippers of U-138 include Kapitänleutnant Wolfgang Lüth from 27 June, 1940 to October, 1940. Lüth also commanded U-9, U-43 and U-181. He won the KNIGHTS CROSS with OAK LEAF CLUSTER, CROSSED SWORDS and DIAMONDS. On 20 October, 1940 command passed to Kapitänleutnant Peter Lohmeyer who also commanded U-19 and U-651. Oberleutnant zur See Franz von Gramitzky took command after Lohmeyer and was Skipper until the boat was lost. He either took command in December 1940 immediately after Lohmeyer, or on 20 April, 1941 after the boat came back out of refit.

U-138 was assigned to the 1st U-BootFlotille based at that time in Kiel, then assigned to the 3rd U-BootFlotille, based at La Rochelle beginning June of 1941. U-138 made several patrols in the North Atlantic, another off the North Channel in October of 1940. She was operating in the area of the Strait of Gibraltar when she was sunk. All survivors taken prisoner. According to German sources, two men were killed. According to U.S. sources, all survived.

SHIPS SUNK BY U-138 UNDER LÜTH
20.09.40	NEW SEVILLA	Brit tnkr	13,801 GRT
20.09.40	BOKA	Pana stmr	5,560 GRT
20.09.40	EMPIRE ADVENTURE	Brit stmr	5,145 GRT
21.09.40	CITY OF SIMLA	Brit stmr	10,138 GRT
15.10,40	BONHEUR	Brit stmr	5,327 GRT
SHIPS SUNK BY U-138 UNDER v. GRAMITZKY
20.05.41	JAVANESE PRINCE	Brit mtrshp	8,593 GRT
SHIPS DAMAGED BY U-138 UNDER LÜTH
13.10.40	DAGRUN	Norw mtrshp	4,562 GRT
(This name and action was intercepted by xB-Dienst. There is no confirmation in any Allied records.)
15.10.40	BRITISH GLORY	Brit mtrshp	6,993 GRT