Potrero del Llano was originally built by Palmers Shipbuilding and Iron Company, Hebburn-on-Tyne as the F.A.

[1] it was interned while docked at Tampico, in Mexico on 10 June 1940 and was seized in 1941 by the Mexican government and renamed Potrero del Llano after a town in Veracruz.

[1] Potrero del Llano was sailing unescorted from Tampico to New York City in May 1942, carrying 6,132 tons of petroleum.

Since only ships of the Mexican Navy were permitted to display the Mexican flag with the eagle in the centre, the flag shown by the Potrero del Llano resembled the Italian one, and having decided that the tanker's position and course meant that she could not be Italian, Suhren decided to sink her.

This established a sound casus belli for the Mexican government to declare war on the Axis powers on 22 May 1942.