The Boeing YC-14 was a twin-engine short take-off and landing

STOL

STOL is an acronym for short take-off and landing, a term used to describe aircraft with very short runway requirements.-Definitions:There is no one accepted definition of STOL and many different definitions have been used by different authorities and nations at various times and for a myriad of...

 (STOL) tactical transport. It was Boeing

Boeing

The Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...

's entrant into the United States Air Force

United States Air Force

The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...

's Advanced Medium STOL Transport

Advanced Medium STOL Transport

The Advanced Medium STOL Transport project was intended to replace the Lockheed C-130 Hercules tactical transport in United States Air Force service with a new aircraft with improved STOL performance...

 (AMST) competition, which aimed to replace the Lockheed C-130 Hercules as the USAF's standard STOL tactical transport. Although both the YC-14 and the competing McDonnell Douglas YC-15

McDonnell Douglas YC-15

|-See also:-References:NotesBibliography* Green, William. The Observer's Book of Aircraft. London. Frederick Warne & Co. Ltd., 1976. ISBN 0-7232-1553-7....

 were successful, neither aircraft entered production. The AMST project was ended in 1979 and replaced by the C-X program.
In mid-1970, the USAF began a paper study, the Tactical Aircraft Investigation (TAI), with Boeing, McDonnell Douglas

McDonnell Douglas

McDonnell Douglas was a major American aerospace manufacturer and defense contractor, producing a number of famous commercial and military aircraft. It formed from a merger of McDonnell Aircraft and Douglas Aircraft in 1967. McDonnell Douglas was based at Lambert-St. Louis International Airport...

, and other companies to look at possible tactical transport aircraft designs.