Operation Deep Freeze is codename for a series of United States missions to Antarctica beginning in 1955. Given the continuing and constant US presence in Antarctica since that date, "Operation Deep Freeze" has come to be used as a general term for US operations in that continent, and in particular for the regular missions to resupply US Antarctic bases, coordinated by the United States military.

Designed to meet a United Airlines requirement for a long-range passenger airliner, the Douglas DC-4 was first flown on June 7, 1938. The prototype was a very ambitious four-engined, pressurized aircraft that was three times the size of its predecessor, the DC-3-a design that proved far too expensive and difficult for civilian airlines to maintain. Douglas revised the design, but by the time it was complete WWII was well underway and development of the aircraft was channeled to the US military. Post-war, the DC-4 became a popular and reliable airliner with major carriers such as National and Northwest Airlines.

Info: R5D-3 Skymaster "Operation Deep Freeze" 56528, US Navy, 1950s