The Boeing Company's Vertol Division (formerly the independent Vertol Aircraft Corporation and now the Boeing Helicopter Company) successfully competed in a 1960 design competition to select a new assault helicopter of the US Marine Corps with a military version of the Model 107-II tandem-rotor helicopter.  Designated Model 107M by the company, the submission in the competition differed from the existing commercial 107 in several details, including up-rated engines, provision for powered folding of the rotor blades, and an integrated loading system.  The submission was adjudged the winner in February 20, 1961, and an initial contract for 14 was placed.

   The first flight of the CH-46A was made on October 16, 1962, and additional contracts in annual increments brought the total number of Sea Knights procured to 624 by the end of 1970.

    Sixty CH-46As were converted to HH-46As for base rescue, fitted with AN/APN-182 doppler radar, external personnel rescue hoist and crash resistant fuel system.
(source: United States Navy Aircraft since 1911 by Gordon Swanborough and Peter Bowers)