a practice of building vehicles to customer specification (a practice still offered by Kenworth today). In 1926, Kenworth expanded its product line, introducing its first bus. In 1927, production was increased from two vehicles a week to three; the same year, manufacturing began in Canada (to avoid import taxes). In 1929, E.K. Worthington retired, with Harry Kent becoming company president. In another change, to accommodate increased demand, Kenworth relocated to a larger factory within Seattle. The onset of the Great Depression hit the company hard; initially in good financial health, a substantial decline in new vehicles and a high rate of vehicle loan defaults forced the company to adapt. In 1932, Kenworth produced its first fire truck; adapted from its commercial truck, Kenworth fire engines were among the heaviest-duty fire apparatus of the time. In 1933, diesel engines became standard equipment, replacing gasoline engines entirely; at the time, diesel fuel cost the price of gasoline. In another design innovation, Kenworth introduced the first factory-produced sleeper cab. In 1935, the Motor Carrier Act was passed, introducing new size and weight regulations for the trucking industry in the United States; to comply with the legislation, Kenworth underwent an extensive redesign of its truck line. To match weight regulations, the new trucks received aluminum cabs and axle hubs; four-spring suspension was introduced, with torsion bars for the rear axles. In 1936, Kenworth introduced the Model 516, its first cabover (COE) truck; the tandem-axle 346 was introduced for 1937. In 1937, Harry Kent died, with Philip Johnson becoming company president. 1940s: War production and company sale In 1939, Kenworth introduced its 500-series trucks, which would form the basis of its commercial truck line into the mid-1950s. By the end of the 1930s, demand for trucks began to recover, with Kenworth producing 226 trucks in 1940. Following the onset of World War II, Kenworth converted to war production, supplying the Army with 4-ton 6x6 M-1 recovery vehicles. In 1943, the company became a supplier for Boeing, manufacturing components for the B–17 and B– 29 bombers. To maintain its government contracts, Kenworth commenced production of the M-1 wrecker at a temporary facility in Yakima, Washington. In total, the company would supply the Army with 1,930 wreckers by the end of World War II; to accommodate the extensive increase in production, Kenworth introduced an assembly line to produce the vehicle. In 1944, company president Phil Johnson died,