base named Fort Brooke) at San Juan Bay. On March 21, 1915, Lt. Marxuach was the officer of the day at El Morro Castle. The Odenwald, built in 1903 (not the German World War II warship of the same name), was an armed German supply ship which tried to force its way out of San Juan Bay and deliver supplies to the German submarines waiting in the Atlantic Ocean. Lt. Marxuach gave the order to open fire on the ship from the walls of the fort. Sergeant Encarnacion Correa then manned a machine gun located along the wall below "La Fortaleza", the governor's residence, and fired warning shots at the ship with little effect. Marxuach then fired a cannon of the Santa Rosa battery in the upper platform of El Morro, in what is considered to be the first shot of World War I fired by the regular armed forces of the United States against any ship flying the colors of the Central Powers, forcing the Odenwald to stop and to return to port, where its supplies were confiscated. The shots ordered by Lt. Marxuach were the first fired by the United States in World War I prior to the official U.S. Congress declaration of war against Germany. The first shots fired after the U.S. Congress declared war on Germany on April 7, 1917 were by U.S. Marines in Apra Harbor, Guam against a launch from the SMS Cormoran. International incident Marxuach's actions became an international incident when the German government accused the United States government of the holding the Odenwald illegally against its will without firing the customary warning shot as required by international law. The United States government responded that the official report of the United States War Department made by Lt. Col. Burnham, the commander of the fortress of El Morro Castle, made it clear that only warning shots were made and that none were aimed at the Odenwald. Eventually, the Odenwald was refitted and renamed SS Newport by the U.S. government and assigned to the U.S. Shipping Board, where it served until 1924, when it was retired. In 1917, the Germans resumed the practice of unrestricted submarine warfare, in part leading to America's entry into the war. Service in the Panama Canal Zone On April 6, 1917, the U.S. Congress declared war on Germany and on May 14, 1917, the Porto Rico Regiment was sent to