On December 8, 1941, the United States declared war on the Empire of Japan. Seattle's location on the Pacific Coast and the existence of important defense industries such as the Boeing Airplane Co. and Todd Shipyards made it a target for enemy attack. Batteries of three-inch guns were placed in the Highland Park Playground in West Seattle and on the 9-hole golf course in Jefferson Park on Beacon Hill. Search light batteries were placed in Woodland Park, Fort Lawton, Jefferson Park, Laurelhurst Playground, Froula Playground, and the Grand Army of the Republic Cemetery near Volunteer Park. A battery of the 304th Barrage Balloon Battalion was based at the Delridge Playground in West Seattle.
A 40 m.m. gun was placed on the tower of the Sears Building on 1st Avenue S, but the soldiers dropped it and bent the barrel. The repair and maintenance of the equipment was done at an Army facility at Westlake Avenue N and N Valley Street at the south end of Lake Union.
Once-open parks were ringed in barbed wire and guarded by sentries. Lawn areas were dug up for gun emplacements and bunkers. Troops used the showers and toilets of field houses, coordinating schedules with residents.
At the end of the war, the Army paid the city for damages done to the park properties.