The 737-400 was launched in 1985 as a stretched 737-300, primarily for use by charter airlines. Piedmont Airlines was the launch customer with an order for 25 aircraft in 1986. The first 400 entered service in 1988 with Piedmont. The 486th and last delivery of the -400 occurred on February 25, 2000 to CSA Czech Airlines.
The 737-400F was not a model delivered by Boeing but a converted 737-400 to an all cargo aircraft. Alaska Airlines was the first to convert one of its -400s from regular service to an aircraft with the ability to handle 10 pallets. The airline has also converted five more into fixed "combi" aircraft for half passenger and freight. These 737-400 Combi aircraft are now in service.