At 06.16 hours on 24 Oct 1939 the unescorted and unarmed Menin Ridge (Master David Emlyn Powell) was hit on the port side below the bridge by one torpedo from U-37 while steaming at 9 knots about 98 miles west of Gibraltar. The U-boat had spotted the ship eight hours earlier and it seems that Hartmann mistook the steering gear on the poop for a stern gun when he decided to attack the darkened vessel without warning, but then waited until dawn after missing with a first torpedo at 01.16 hours. Due to the heavy cargo, the ship broke up and sank immediately after being hit and only five crewmen managed to rescue themselves by clinging to wreckage. The master and 19 crew members were lost. The U-boat remained submerged after the attack because a ship was seen to approach the sinking position.

The ship was Ledbury which picked up one of the survivors about three hours after the attack and then launched her starboard lifeboat to rescue the other four. However, before they could be taken aboard the ship was shelled and sunk by U-37. Subsequently the U-boat approached the lifeboat with the survivors of both ships to question them before leaving the area. The Germans had asked about the name of the first ship sunk, but misunderstood it as Mainedge. At about 11.30 hours, all survivors were picked up by the American motor merchant Crown City (Master W.E. Carley) and landed at Gibraltar later that day.