The U.S. Navy selected a Renton, WA, location for the manufacture of its new XPBB-1 Sea Ranger long-range flying boat patrol bomber on 09/02/1941. In 1941, this 95-acre portion of Renton was marsh, edging the southern coast of Lake Washington; according to a Boeing Company historical reference, this southern site was important for the testing of the flying boat: "The waterfront site provided natural protection from prevailing winds, so it was easier to launch seaplanes directly from the plant" (See "History: XPBB-1 Sea Ranger,"Accessed 01/05/2011.) Four-hundred-fifty-thousand yards of soil and landfill were required to provide level ground on which to build the sprawling plant which opened in 1942. The first (and only) XPBB-1 was flight tested on 07/09/1942. Later in the war, the US Army swapped a production facility in Kansas City, MO, with the Navy and took over the Renton plant; here, Boeing assembled 1,119 B-29 bombers for the US Army Air Forces (USAAF), planes crucial for winning World War II. As of 05/21/2008, workers at Boeing's Renton factory were producing 30 737s a month on two production lines. Another line in this facility was set to build P-8A U.S. Navy Poseidon anti-submarine planes at that time. Plans were to build 113 P-8As for the Navy by 2017.
The US Government directed this plant's construction before America's official entry into World War II on 12/07/1941. In part to bolster the defenses of Britain and France, the US had provided resources and materiel to both countries, causing a need to ramp up military production within the US. This pre-war build-up (starting c. 1937-on) of manufacturing facilities and military bases proved prescient.