At 20.34 hours on 15 June 1942 the neutral Frimaire was hit by two of three torpedoes from U-68, capsized and sank by the stern northeast of Barranquilla, Colombia. Merten had seen French nationality markings without the yellow boarder for the Vichy government and correctly identified the tanker, but did not know about neutral traffic in this area and assumed that the ship had been seized and was en route to Panama. Only after the sinking he was told by the BdU that this had been a Vichy French tanker operating under Portuguese charter and his attack had been wrong.