Before the Spanish Civil War, he learned naval carpentry and worked aboard a ship. In the war he fought with the Republican side and was severely wounded at the Battle of Brunete. At the end of the war, he was in Barcelona. Thanks to an acquaintance, he was freed and returned to Catasueiro. However, due to the hardship of the postwar period, he decided to embark for the United States, where he entered illegally. He lived in New York and enlisted in the US Army on March 19, 1943. He served in the 16th Infantry Regiment No. 1 of the 1st Division, the “Big Red One”. He was a “Private First Class”. Otero Martínez died at “Omaha Beach” on June 6, 1944. He was the only Spaniard to take part in the Normandy Landings. He received the Purple Heart Medal, awarded to all soldiers wounded or killed in combat.
He was initially buried in the American cemetery in St Laurence (France) and his remains were later moved to the churchyard of San Xoán de Sabardes (O Freixo, Serra de Outes). In 2014, a plaque in his honor was inaugurated on Monte de San Pedro, A Coruña (Source: Antonio Osende Barallobre, Manuel Otero Martínez, un gallego en “Omaha Beach” (2016)).