The first five boats sailed independently in October 1939 from bases in NW Germany, sailing northabout around the coast of Scotland in order to reach the
Western Approaches. The last boat, , which was delayed in departing, was ordered to take the southabout route through the
Channel; this was more dangerous, but was deemed practicable. In the event
U–40 became trapped by the Allies' Channel defences, the
Dover Barrage; on 13 October she struck a mine and was destroyed. The remaining five boats under Hartmann’s command took station in the Western Approaches. The German signals intelligence branch,
B-Dienst, which had penetrated British naval codes, was able to give notice of a convoy (KJF 3) from the
Caribbean and BdU instructed the pack to intercept. Three boats found the convoy and attacked, while a fourth failed to make contact. The fifth, , met a freighter sailing independently; she attacked, but was counter-attacked by two destroyers that came to the scene and was destroyed. The attack on KJF 3 was an ad hoc affair (Blair describes it as "an uncoordinated free for all"); though four ships were sunk, one of the attacking boats, was destroyed by the convoy escorts. A second convoy, HG 3 from
Gibraltar, was detected by
B-dienst and Hartmann’s boats were again ordered to intercept. made contact and shadowed while the other two closed. The attack sank three ships without loss to the attackers. Following this the boats were relieved, and returned home. ==Aftermath==