What artillery battalion fired the last round in World War 1?

The first shot of World War I by the U.S. was fired in Puerto Rico on the 21st of March 1915, ordered by a Puerto Rican serving in the U.S. Army, Lieutenant Teofilo Marxuach. Lt. Marxuach was officer of the day at El Morro Castle, at the entrance to San Juan Bay. An armed supply ship for German submarines in the Atlantic, the Odenwald, tried to force its way out of the bay. Lieutenant Marxuach ordered his men to open fire from the walls of the fortress and forced the ship to return to port and be interned. http://www.houseofpuertorico.com/articles/PR-A_Commonwealth.htm