First of what was to become a pair of instantly recognizable heavy transport helicopters, the Boeing Vertol CH-46 Sea Knight has been a fixture of US military operations since its beginnings in the 1960s. Nicknamed the 'Phrog', the Sea Knight's main identifiable feature is its tandem twin-rotor configuration which gives it stability without the need for a tail rotor and which provides extraordinary lift capabilites. These virtues allowed the CH-46 to see combat for the first time in the Vietnam War with the US Marine Corps as an assault transport for amphibious and land operations, where it was often fitted with armor and weaponry. It was also adopted by the US Navy which also uses them for search and rescue (SAR) and minesweeping duties as well as a number of other foreign operators including Canada, Sweden, Saudi Arabia and Japan where it is license-built by Kawasaki. Today it remains in service with the USMC although scheduled to be eventually replaced by the tilt-rotor V-22.

Twin-rotor designs had been a specialty of the Vertol (previously known as Piasecki) corporation which designed the Model 107 whose prototype first flew on 22 April 1958. The US Army saw interest but it was the USMC which first adopted it from a revised Model 107M leading to the initial CH-46A production units. It was improved as the CH-46D with a new powerplant which increased payload and later the CH-46F with newer avionics. Most, however, have been upgraded into the extensively modernized CH-46E, the definitive USMC variant which is still in service today. US Navy versions include the UH-46A and -46D used for resupply missions, the HH-46A and -46D for SAR duties, and the RH-46 minesweepers. Canadian versions are known as the CH-113 Labrador, used mostly for SAR by the Canadian Coast Guard.