"U-65"s first war patrol began on 9 April 1940 when she left her home port of Wilhelmshaven. For 36 days she patrolled the North Sea and the waters off the coast of Norway, participating in the invasion of that country. During this time, she sank no enemy vessels. On 13 April, the U-boat attacked a group of British destroyers north of Bergen, Norway; but her torpedoes failed to detonate, the destroyers counter-attacked, causing some minor damage to the submarine. "U-65" was able to escape the attack, she returned safely to Wilhelmshaven on 14 May.