On January 15, 1937, the Beechcraft Model 18 made its first demonstration flight at the factory in Wichita, Kansas, and it continued in production for thirty-two years. This low-wing, all-metal, twin-engine monoplane was originally intended as a six-to-eight-passenger executive or feeder airline transport. As the years passed, however, the Model 18 was adapted to many uses and, in all, thirty-two different versions were produced.

World War II brought more orders for military versions of the Beech 18S from the United States and foreign governments for a wide range of uses. About 90 percent of the U.S. Air Force's navigators and bombardiers received their training on AT-7s and AT-11s respectively. The U.S. Navy SNB-1 was similar to the AT-11, the SNB-2 to the AT-7. The JRB-1 was a radio-control airplane for target or drone aircraft. The Navy's personnel transports similar to the C-45 were known as JRB2, JRB-3, and JRB-4.

With the end of the war came the end of military production, although many of these aircraft remained in service for years. By October 1945 Beech was back into full commercial aircraft production. The first aircraft off the line was the newest model, the D18S, which incorporated a number of improvements. Structural modifications allowed for an increase in maximum weight and new landing gear, brakes, and tires were installed. Two 450-hp Pratt & Whitney Wasp, Jr., engines with Hamilton Standard constant speed propellers powered the D18S. It was the premier executive transport among businessmen and it was also used by the new local service airlines that emerged after the end of World War II.

On December 10, 1953, the prototype of the Super 18, the last version of the Beech 18, made its first flight. The last three production aircraft were delivered in November 1969. More than 9,000 Model 18s were produced since 1937, and, in 1970, more than 2,000 were still being flown in the United States alone.