The US investigation concluded for a collision with the Thomson Lykes cargo ship. The sub was effectively compelled to surface to reload the batteries. However, the dimensions given by the Thomson Lykes do not coincide with those of the Surcouf.
The French claimed it was sunk by error by a PBY. There was effectively a report of a sunken sub by Cats in the vicinity of the place where it disappeared. Furthermore, German archives do not report a sub sunk in the Caraïbes by this time (night of february 18 to 19, 1942).