Glenn L. Martin began flying planes in 1909 in Santa Ana, California, moved to Los Angeles in 1912 and Cleveland in 1917, and later relocated his company to Middle River. A pioneering birdman, he built the first U.S. Army training plane in 1913 and, by the start of World War I, introduced the MB-1 bomber, the first all-American military plane. In 1929 he chose Middle River for a new plant because of its proximity to Baltimore and Washington, railroad access, workforce, and year-round flying weather. Industrial architect Albert Kahn designed Plant No. 1 there specifically for metal airplane construction, and manufacturers considered it among the most modern in the country. One of the first aircraft built there was the XTSM-1 dive bomber, among the earliest of its kind in the world, and pilots tested Martin seaplanes for the U.S. Navy at Strawberry Point on Stansbury Creek. In 1939 the company designed the first intercontinental airliner, the China Clipper, also known as the Martin M/130, a flying boat used by Pan Am to carry passengers to Asia, the Pacific Rim, and Africa. That same year Martin and Kahn built the Glenn L. Martin Airport as a testing and exit factory for military aircraft manufactured at the plant, with four runways intersecting in a star-like pattern. During the World War II era, the company grew from 4,100 workers in 1939 to 53,000 in 1942 as workers migrated from the rural South, Pennsylvania, and the Midwest, and women and African-Americans contributed to the wartime effort. Housing developments were built within one mile of the plants, and many families still live there. At the dawn of World War II, the company produced 3,572 B-26 Marauder medium bombers in Plant No. 2, built in 1940-1941 across from Plant No. 1 on Eastern Boulevard and also designed by Kahn. After World War II, production shifted from nearly all military aircraft to a mix of commercial and military planes. After Martin's death in 1955, planes continued to be built at Middle River until 1960. In 1961 the company merged with the American-Marietta Company to become Martin Marietta. In 1971 the State of Maryland bought the Glenn L. Martin Airport, including the original Plant No. 1, and the airport came to serve general aviation and the Air National Guard. In 1990 the Glenn L. Martin Maryland Aviation Museum opened at Martin State Airport.