The "G-1" military flight jacket is the commonly accepted name for the fur-lined-collar World War II-era flight jacket of the United States Navy, Marine Corps, and Coast Guard. A similar jacket used by the United States Army Air Corps/United States Army Air Forces was usually called the A-2 jacket.
The G-1 remains a current uniform-issue item in naval aviation for officer and enlisted aviation personnel on flying status in the U.S. Navy, U.S. Marine Corps and U.S. Coast Guard (i.e., Naval Aviator, Naval Flight Officer, Naval Flight Surgeon, Naval Aircrewman, etc.) and is arguably best known as the leather flight jacket worn by Tom Cruise in the film Top Gun.
More technically, the jacket may be considered the U.S. Military flight jacket developed in 1947 and used in the Korean War, since the term "G-1" was not used as a label for this fur-collared military-issued jacket until after World War II. However, the term "G-1" has come to be used for this style of naval leather flight jacket. Prior to the end of World War II, and starting in 1940 when it was officially named by the U.S. Navy, the jacket had the military spec number of M-422.
This jacket was brought to use by the U.S. Navy in the 1930s, and standardized by the Navy in 1940 as the M-422A. In 1943 this jacket, named by the Army Air Forces and the Navy as the ANJ-3 (Army Navy Jacket 3), replaced the iconic Army Air Forces A-2 jacket, the most famous of U.S. Military jackets, hence the name of ANJ-3 (vs. A-2). The M-422A replacement of the loved and famous A-2 was, however, in the form of a non-fur-collared version of the "G-1", currently referred to for obvious reasons as the G-2. In 1988, the U.S. Air Force reinstated the A-2 jacket for all USAF flight crew personnel.