On April 10, 1917, four days after the United States declared war on Germany, an explosion at the Eddystone Ammunition Corporation's artillery shell plant in Eddystone, Pennsylvania, killed 139 people. The majority were women and girls who worked in the loading room, loading shells with black powder. 55 of the victims could not be identified and were buried in a mass grave. Hundreds more were injured. The victims were arguably among the first American casualties of World War I.