On May 14, 1942 the Mexican steam tanker Potrero del Llano, was headed to New York loaded with 6,132 barrels of petroleum. Because Mexico was neutral the vessel was in compliance with international law which stated that vessels of neutral countries should be fully illuminated and properly display the flag of their country of origin. Nevertheless the Potrero del Llano was torpedoed and by U-564 off the east coast of Florida. The oil tanker sank with the loss of fifteen lives.

The Mexican government protested and broke diplomatic relations with Nazi-Germany. Two weeks later U-106 torpedoed another Mexican oil tanker, Faja de Oro under similar circumstances off the Florida keys. Ten lives were lost and 27 survived. The unprovoked attacks caused outrage amongst the Mexican people who took to the streets to protest. On May 28, President Camacho addressed the Mexican Congress. In his address speech President Camacho stated that “nothing stopped the aggressors” indeed it appeared that neither humanitarian or international laws had been observed by the totalitarian power. On June 1st the President declared that a “state of war” existed between Mexico and the Axis Powers.

Thousands of people in Miami watched the Potrero del Llano burn for hours before it sank.

However, as is often the case with international incidents there are two conflicting sides to the story. An official statement by the German government at the time claimed that the Potrero had been in violation of international law by traveling in a war-zone without lights and that the ships flag, which was painted on both sides of the vessel, was not properly lighted. This contradicts eye witness statements that the ship was adequately illuminated in order to make its flag visible.

Reinhard Suhren.

The German government claimed that this information was based on a report from the U-boat’s commander Reinhard Suhren. Suhren, an Iron Cross decorated commander, also said that he mistook the Mexican flag for an Italian flag and that because an Italian ship could not be in Florida waters he made the decision to sink the unknown ship. The Italian flag appears almost the same as the Mexican flag. However the Mexican flag has an eagle at its center. At that time only vessels of the Mexican Navy were permitted to display the eagle emblem. Moreover, the tanker had its name and the word Mexico painted in huge white letters on both sides. Apparently U-564 also followed the Potrero for more than half an hour before firing its torpedoes. In total four Mexican oil tankers were sunk by U-boats in WW2.

The question of whether or not U-boats intentionally attacked vessels of neutral countries is up for debate. However the attacks by U-106 and U-564 were far from isolated incidents. After Brazil broke off diplomatic relation with Axis Powers, hardly an act of aggression, its ships were attacked by U-boats. During the month of August 1942, U-507 sunk six Brazilian ships with the loss of 877 lives. Brazil declared war on Germany and Japan on August 22.

The Potrero del Llano drifted north of Miami Beach, however the 7,588 ton shipwrecked tanker's final resting place is unknown. 

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