Also known by the company designation PV-3, this was the first American tandem rotor helicopter. 2 of these aircraft were produced, 1 for static and dynamic tests and 1 for U.S. Navy trials.

Source: AHS Calendar November 2013

Note: A review of many different reference sources indicates that this aircraft must have flown in 1946 instead of 1947. This would also be consistent with the production aircraft (HRP-1) flying in August 1947