Piasecki H-21B “Workhorse” “P” Listings Piasecki HUP-3 “Retriever”

Piasecki HUP-1 “Retriever”
USN tandem-rotor utility helicopter

Archive Photos ¹

Piasecki HUP-1 “Retriever” on display circa 2005 at the USS Hornet Museum, Alameda Point, Alameda, California (John Shupek photo copyright © 2005 Skytamer Images)

Overview ²

  • H-25/HUP Retriever
  • Role: Utility helicopter
  • Manufacturer: Piasecki Helicopter
  • First flight: March 1948
  • Introduction: 1949
  • Retired: 1964
  • Primary users: United States Navy, United States Army, Royal Canadian Navy, French Navy
  • Number built: 339

The Piasecki H-25 “Army Mule”/HUP “Retriever” was a compact single radial engine, twin overlapping tandem rotor utility helicopter developed by the Piasecki Helicopter Corporation of Morton, Pennsylvania during the late 1940s and produced during the early 1950s. The company changed its name in the 1956 to Vertol Aircraft Corporation and subsequently was bought by Boeing Aircraft Company in 1960, and became Boeing-Vertol.

Design and Development ²

The design was a product of a competition by the U.S. Navy in 1945 for a compact utility/rescue helicopter to operate from Navy ships including aircraft carriers, battleships, and cruisers. The prototype was designated by the Navy as the XHJP-1, and first flew in March 1948. It was selected by the Navy for production, as the HUP-1 in a side-by-side flight evaluation against the Sikorsky XHJS-1. It entered service with the Navy and USMC from 1949.

Operational History ²

Versions of the HUP built for the U.S. Army were designated H-25 “Army Mule”. The tandem overlapping rotor configuration was a development by Piasecki and was used in future helicopter designs by the company and successors including the H-21, HRB-1/CH-46, and CH-47.

The design featured two three-bladed, 35-foot-diameter (11 m) rotors in tandem in which blades could be folded for storage in ships' hangars. The HUPs were powered by a single Continental R975-46 radial engine, with a take-off rating of 550 hp (410 kW). To provide rescue without crew assistance, an electrically operated door, available after folding the copilot's seat forward, opened through which a rescue sling could be lowered from an overhead winch.

The HUP was produced for the Navy in four versions: HUP-1, -2, and -3. The HUP-2 was the first production helicopter equipped with an auto-pilot. The US Navy also tested a system called 'Raydist that allowed an unmanned HUP-2 to be directed from a ground station and by radio ordered to hover with in 5 feet of the desired point. Edo tested a HUP-2 with a fiberglass hull and outrigger floats for amphibious operations. In addition to those delivered to the U.S. Navy and Army the HUP/H-25 helicopter was also delivered to the Canadian and French Navies. A total of 339 aircraft were delivered over the 20-year life of the aircraft.

The US Army H-25 designation was adopted by the other services in 1962. The final units were withdrawn from US service in 1964. It also served with the French Navy from 1953 to 1965.

Variants ²

  • XHUP-1: The first two prototypes.
  • HUP-1: Utility transport, search and rescue helicopter for the US Navy, powered by a 525 hp (391 kW) Continental R-975-34 piston engine.
  • HUP-2: Improved version, powered by a 550 hp (410 kW) Continental R-975-46 piston engine. Later redesignated UH-25B in 1962.
  • HUP-2S: This designation was given to 12 HUP-2's. The HUP-2S was an anti-submarine warfare helicopter, fitted with a dunking sonar equipment.
  • HUP-3: Utility transport helicopter for the US Navy, powered by a 550 hp (410 kW) Continental R-975-46A piston engine. Similar to the H-25A “Army Mule”, later redesignated UH-25C in 1962.
  • H-25A “Army Mule”: Utility transport helicopter for the US Army, powered by a 550 hp (410 kW) Continental R-975-46A piston engine, fitted with large doors, power-boosted controls and strengthened floors. It was called the H-25A “Army Mule”. Seventy were delivered from 1953, but they proved unsuitable for front-line use, with 50 transferred to the Navy from 1955, and the remaining helicopters used for training, being withdrawn completely from Army service by 1958.

Operators ²

  • France: French Navy
  • United States: US Army; US Navy

Specifications (HUP-3) ²

General Characteristics

  • Crew: 2 pilots
  • Capacity: 4 passengers
  • Length: 56 ft 11 in (17.35 m)
  • Rotor diameter: 35 ft 0 in (10.67 m)
  • Height: 12 ft 6 in (3.81 m)
  • Disc area: 1,924 ft² (179 m²)
  • Empty weight: 3,928 lb (1,782 kg)
  • Loaded weight: 5,750 lb (2,608 kg)
  • Max. takeoff weight: 6,100 lb (2,767 kg)
  • Powerplant: 1 × Continental R-975-46A radial, 550 hp (410 kW)


  • Maximum speed: 105 mph (169 km/h)
  • Range: 340 mi (547 km)
  • Service ceiling: 10,000 ft (3,048 m)
  • Rate of climb: 100 ft/min (5.01 m/s)
  • Disc loading: 3 lb/ft² (15 kg/m²)
  • Power/mass: 0.09 hp/lb (0.16 kW/kg)


  • Photos copyright © 2005 Skytamer Images (John A. Shupek)
  • Wikipedia (Background information, specifications, etc.), Piasecki H-25

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