10/31/2009. First of the American light twin-engined aircraft of post-war design, the prototype Model 50 Twin Bonanza flew on November 15, 1949. The US Army bought 105 Model H50s, designating them L-23D. These were fitted with two 340 hp Lycoming GSO-480-BIB6 supercharged six-cylinder horizontally-opposed air-cooled engines. Furthermore, all but two of the earlier bought 55 L-23As and 40 L-23Bs were converted to L-23Ds. The L-23D was redesignated U-8D in 1962.