The Piasecki HUP Retriever or H-25 Army Mule, later UH-25, is a compact single

radial engine The radial engine is a reciprocating engine, reciprocating type internal combustion engine, internal combustion engine configuration in which the cylinder (engine), cylinders "radiate" outward from a central crankcase like the spokes of a wheel. ...

, twin overlapping

tandem rotor A tandem-rotor aircraft is an aircraft with two large helicopter rotor assemblies mounted one in front of the other in the horizontal plane. This configuration is mainly used for large cargo helicopters. Such aircraft are often informally referr ...

utility

helicopter A helicopter is a type of rotorcraft in which Lift (force), lift and thrust are supplied by horizontally spinning Helicopter rotor, rotors. This allows the helicopter to VTOL, take off and land vertically, to hover (helicopter), hover, and ...

developed by the

Piasecki Helicopter Corporation The Piasecki Helicopter Corporation was an American designer and manufacturer of helicopters in Philadelphia and nearby Morton, Pennsylvania, in the late 1940s and the 1950s. Its founder, Frank Piasecki, was ousted in 1956 and started a new co ...

of Morton, Pennsylvania. Designed to a

United States Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...

specification, the helicopter was produced from 1949 to 1954, and was also used by the

United States Army The United States Army (USA) is the primary Land warfare, land service branch of the United States Department of Defense. It is designated as the Army of the United States in the United States Constitution.Article II, section 2, clause 1 of th ...

and foreign navies. The HUP/H-25 was the first helicopter to be produced with an

autopilot An autopilot is a system used to control the path of a vehicle without requiring constant manual control by a human operator. Autopilots do not replace human operators. Instead, the autopilot assists the operator's control of the vehicle, allow ...

and also the first to perform a loop.

Design and development

The design was a product of a competition by the U.S. Navy in 1945 for a compact utility/rescue helicopter to operate from ships including aircraft carriers, battleships, and cruisers. Either 2 or 3 prototypes—designated PV-14 by the factory and XHJP-1 by the Navy—were built and subjected to a side-by-side flight evaluation against the 3 prototypes of the Sikorsky XHJS-1; however, the XHJS was fundamentally a scaled-up version of the

Sikorsky H-5 The Sikorsky H-5 (initially designated R-5 and also known by company designations S-48, S-51 and VS-327Fitzsimons, Bernard, (general editor). ''Illustrated Encyclopedia of 20th Century Weapons and Warfare'' (London: Phoebus, 1978), Volume 20, p ...

, and the increased weight and size magnified the design's problems with maintaining proper weight and balance under varying loading conditions. The Piasecki won the competition, and with the introduction of the aircraft configuration letter "U" for Utility in the 1950s, the aircraft was ordered for production as the HUP-1. The design featured two three-bladed, rotors in tandem in which blades could be folded for storage; the relatively small rotor diameter allowed the aircraft to use aircraft carrier elevators with its blades fully extended. 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 Boeing CH-47 Chinook is a tandem-rotor helicopter originally developed by American rotorcraft company Piasecki Helicopter, Vertol and now manufactured by Boeing Defense, Space & Security. The Chinook is a Military transport helicopter, heav ...

. The original HUP-1 was powered by a single Continental R-975-34 radial engine, with a take-off rating of , while later versions used the uprated R-975-42 or R-975-46A with . To aid

search and rescue Search and rescue (SAR) is the search for and provision of aid to people who are in distress or imminent danger. The general field of search and rescue includes many specialty sub-fields, typically determined by the type of terrain the search ...

(SAR) operations, the aircraft was equipped with an overhead winch capable of lifting 400 lb (181 kg), which could lower a rescue sling through an electrically-operated door available after the copilot's seat was folded forward. During a flight demonstration of its capability to withstand high

g-force The g-force or gravitational force equivalent is a Specific force, mass-specific force (force per unit mass), expressed in Unit of measurement, units of standard gravity (symbol ''g'' or ''g''0, not to be confused with "g", the symbol for ...

, the type became the first helicopter to perform a loop, albeit unintentionally.

Operational history

The aircraft first entered service in February 1949 with the delivery of the first of 32 HUP-1 aircraft to the US Navy. The improved HUP-2 (Piasecki designation PV-18) was soon introduced with a more powerful engine, deletion of the inward-canted horizontal stabilizer endplate fins, and various minor changes in equipment; a sub-variant equipped with dunking

sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances ( ranging), communicate with or detect objects o ...

for

anti-submarine warfare Anti-submarine warfare (ASW, or in the older form A/S) is a branch of underwater warfare that uses surface warships, aircraft, submarines, or other platforms, to find, track, and deter, damage, or destroy enemy submarines. Such operations ar ...

was given the designation HUP-2S. The HUP-2 was the first production helicopter equipped with an

. The US Navy also tested a

radio navigation Radio navigation or radionavigation is the application of radio waves to geolocalization, determine a position of an object on the Earth, either the vessel or an obstruction. Like radiolocation, it is a type of Radiodetermination-satellite servi ...

system called ''Raydist'' that allowed an unmanned HUP-2 to be directed from a ground station and by radio ordered to hover within of the desired point.

Edo Edo (), also romanized as Jedo, Yedo or Yeddo, is the former name of Tokyo. Edo, formerly a (castle town) centered on Edo Castle located in Musashi Province, became the '' de facto'' capital of Japan from 1603 as the seat of the Tokugawa shogu ...

tested a HUP-2 with a fiberglass hull and outrigger floats for amphibious operations. An upgraded version of the HUP-2 was built for the

US Army The United States Army (USA) is the primary land service branch of the United States Department of Defense. It is designated as the Army of the United States in the United States Constitution.Article II, section 2, clause 1 of the United Stat ...

and designated as the H-25A Army Mule, but most were quickly withdrawn from Army service and converted for naval use under the designation HUP-3. 330-ps-7528-usn-681155 16661806845 o

In 1954, the

Royal Canadian Navy The Royal Canadian Navy (RCN; , ''MRC'') is the Navy, naval force of Canada. The navy is one of three environmental commands within the Canadian Armed Forces. As of February 2024, the RCN operates 12 s, 12 s, 4 s, 4 s, 8 s, and several auxiliary ...

received three former US Army H-25A aircraft, which were modified and redesignated on delivery to conform to US Navy HUP-3 standards. The aircraft were used aboard HMCS ''Labrador'' for

and varied utility duties, and were later used to support construction at

Distant Early Warning Line The Distant Early Warning Line, also known as the DEW Line or Early Warning Line, was a system of radar stations in the northern Arctic region of Canada, with additional stations along the north coast and Aleutian Islands of Alaska (see List o ...

radar sites. The helicopters were subsequently posted to NAF Patricia Bay and naval air station HMCS ''Shearwater''; after the last two were stricken from inventory on 18 January 1964, one aircraft was donated to a technical school and the other two were sold as surplus. The US Army H-25 designation was adopted by the US Navy in 1962 on introduction of the

1962 United States Tri-Service aircraft designation system The Tri-Service aircraft designation system is a unified system introduced in 1962 by the United States Department of Defense for designating all U.S. military aircraft. Previously, the U.S. armed services used United States military aircraft de ...

. The final units were withdrawn from US service in 1964. It also served with

French Naval Aviation French Naval Aviation (often abbreviated in French to: (contraction of ), or , or more simply ) is the naval air arm of the French Navy. The long-form official designation is . Born as a fusion of aircraft carrier squadrons and the naval pat ...

(Aeronavale) from 1953 to 1965. A total of 339 aircraft were delivered during the 6-year production run. A large number of surplus US Navy aircraft later appeared on the US civil registry, and at least seven were transferred to the

French Navy The French Navy (, , ), informally (, ), is the Navy, maritime arm of the French Armed Forces and one of the four military service branches of History of France, France. It is among the largest and most powerful List of navies, naval forces i ...

. On 7 November 2009, former US Navy HUP-1, BuNo ''124925'', civil registration number ''N183YP'', collided with high-voltage power lines in

Adelanto, California Adelanto (Spanish for "Advance") is a city in San Bernardino County, California, United States. It is approximately northwest of Victorville in the Victor Valley area of the Mojave Desert, in the northern region of the Inland Empire.Linthicum ...

; the subsequent crash and post-crash fire killed all 3 occupants and substantially damaged the aircraft. Operated in association with Classic Rotors, the accident aircraft was the only airworthy example in the world. The

National Transportation Safety Board The National Transportation Safety Board (NTSB) is an independent U.S. government investigative agency responsible for civil transportation accident investigation. In this role, the NTSB investigates and reports on aviation accidents and inci ...

attributed the crash to ''"The pilot’s failure to maintain clearance from powerlines during en route flight."''

Variants

;XHJP-1 :Prototype, powered by a Continental R-975-34 piston engine, equipped with large sloping endplate fins on the horizontal stabilizers. Piasecki-Vertol designation was PV-14. 2 or 3 produced. ;HUP-1 :Utility transport and search and rescue helicopter for the

US Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...

, largely similar to XHJP-1, Piasecki designation was PV-18. 32 built. ;HUP-2 :Improved version, Continental R-975-42 piston engine, horizontal stabilizer endplate fins eliminated. 165 built for the US Navy, 15 for French Aeronavale. Redesignated UH-25B in 1962. ;HUP-2S :Anti-submarine warfare version of HUP-2 fitted with dunking sonar. 12 built. ;HUP-3 :Naval utility conversion of H-25A aircraft transferred from US Army: 50 to US Navy, 3 to Royal Canadian Navy. ;H-25A Army Mule :Utility transport helicopter for US Army, similar to HUP-2 but powered by a Continental R-975-46A piston engine, and fitted with large doors, power-boosted controls, and strengthened floors. 70 were delivered from 1953, but they were unsuitable for front-line use, with 53 transferred to the Royal Canadian and US Navies in 1954–1955, and the remaining helicopters used for training, being withdrawn from army service by 1958.Harding 1990, pp. 197–198. ;UH-25B :HUP-2 redesignated after 1962. ;UH-25C :HUP-3 redesignated after 1962.

Operators

; *

; : *

Surviving aircraft

For surviving aircraft, hyphenated numbers are original US Army Serial Numbers; six-digit numbers are original US Navy Bureau of Aeronautics (BuAer) Bureau Numbers (BuNo). All 50 H-25A/HUP-3 aircraft transferred from the US Army to the US Navy were given new bureau numbers; 3 aircraft transferred to the Royal Canadian Navy were redesignated, but retained their original US Army serial numbers.

Canada

;On display * UH-25B (HUP-2) 128529 at

Shearwater Aviation Museum The Shearwater Aviation Museum is an aviation museum located at CFB Shearwater in Shearwater, Nova Scotia. The museum acquires, conserves, organizes, researches and interprets to Canadian Forces personnel and the public at large for their study, ...

in Shearwater, Nova Scotia. This aircraft has been restored to the appearance of ''51-16621'', the first Royal Canadian Navy HUP-3. * UH-25C (HUP-3), 51-16623 -

Canada Aviation and Space Museum The Canada Aviation and Space Museum () (formerly the Canada Aviation Museum (''Musée de l'aviation du Canada'') and National Aeronautical Collection (''Collection aéronautique nationale'')) is Canada's national aviation history museum. The m ...

in Ottawa, Ontario.

Netherlands

* UH-25B (HUP-2), 130076 (construction number 253) – Baris Business Park roadway roundabout in

Rotterdam Rotterdam ( , ; ; ) is the second-largest List of cities in the Netherlands by province, city in the Netherlands after the national capital of Amsterdam. It is in the Provinces of the Netherlands, province of South Holland, part of the North S ...

. This aircraft was originally used by the US Navy and was later transferred to the

United Kingdom

* UH-25C (HUP-3), 51-16622 – displayed at

The Helicopter Museum The Helicopter Museum in Weston-super-Mare, North Somerset, England, is a museum featuring a collection of more than 80 helicopters and autogyros from around the world, both civilian and military. It is based at the southeastern corner of the fo ...

in Weston-super-Mare, England, wearing Canadian markings.

United States

;On display ;;H-25A Army Mule * 51-16616 –

United States Army Aviation Museum The United States Army Aviation Museum is an aviation museum located on Fort Novosel near Daleville, Alabama. It has the largest collection of helicopters held by a museum in the world.Phillips 1992, p. 37.Purner 2004, p. 204. The museum feature ...

in Fort Rucker, Alabama. ;;HUP-1 * 124915 – USS Hornet Museum in Alameda, California. ;;UH-25B (HUP-2) * 128479 –

American Helicopter Museum The American Helicopter Museum & Education Center (AHMEC) is located at 1220 American Boulevard, West Chester, Pennsylvania, United States. The transport museum focuses on the history, science and technology of rotary wing aviation. The collect ...

in West Chester, Pennsylvania. * 128517 – Wings of Freedom Aviation Museum in Horsham, Pennsylvania. * 128519 –

Intrepid Sea, Air & Space Museum The ''Intrepid'' Museum (originally the ''Intrepid'' Sea, Air & Space Museum) is a military and maritime history museum in New York City, United States. It is located at Pier 86 at 46th Street (Manhattan), 46th Street, along the Hudson River, ...

in New York City, New York. * 128596 –

Flying Leatherneck Aviation Museum The Flying Leatherneck Aviation Museum is a United States Marine Corps aviation museum currently located at the Orange County Great Park in Irvine, California. The museum contains exhibits and artifacts relating to the history and legacy of Unit ...

in San Diego, California. * 130059 –

USS Midway Museum The USS ''Midway'' Museum is a historical naval aircraft carrier museum in San Diego, California, United States, located at Navy Pier. The museum consists of the aircraft carrier . The ship houses an extensive collection of aircraft, many of ...

in San Diego, California. * 130082 – on the deck of the

USS Iowa Museum The Battleship USS ''Iowa'' Museum is a maritime museum located at the Port of Los Angeles in San Pedro, Los Angeles, California, United States. The museum's main artifact is the USS ''Iowa'' (BB-61), lead ship of the ''Iowa'' class of battle ...

in San Pedro, California. ;;UH-25C (HUP-3) * 147595 –

Pima Air & Space Museum The Pima Air & Space Museum is an aerospace museum in Tucson, Arizona, US. It features a display of nearly 400 aircraft spread out over on a campus occupying . It has also been the home to the Arizona Aviation Hall of Fame since 1991. Overv ...

in Tucson, Arizona. * 147600 –

Air Zoo The Air Zoo, founded as the Kalamazoo Aviation History Museum, is an aviation museum and indoor amusement park next to the Kalamazoo-Battle Creek International Airport in Portage, Michigan. The Air Zoo holds many historical and rare aircraft, inc ...

in Kalamazoo, Michigan. * 147607 –

National Naval Aviation Museum The National Naval Aviation Museum, formerly known as the National Museum of Naval Aviation and the Naval Aviation Museum, is a military and aerospace museum located at Naval Air Station Pensacola, Florida. Founded in 1962 and moved to its cur ...

in Pensacola, Florida. * 147628 –

Mid-America Air Museum The Mid-America Air Museum is an aerospace and aircraft museum located at the Liberal Mid-America Regional Airport in Liberal, Kansas, United States. The Mid-America Air Museum is the largest aircraft museum in Kansas. It has on display over ...

in Liberal, Kansas. * 51-16621 – Classic Rotors in Ramona, California. As of December 2019, this is the only Piasecki Helicopter-manufactured aircraft with valid FAA

aircraft registration An aircraft registration is a code unique to a single aircraft, required by international convention to be marked on the exterior of every civil aircraft. The registration indicates the aircraft's country of registration, and functions much li ...

. This former Royal Canadian Navy aircraft is reportedly the last HUP/H-25 capable of being restored to

airworthy In aviation, airworthiness is the measure of an aircraft's suitability for safe flight. Initial airworthiness is demonstrated by a certificate of airworthiness issued by the civil aviation authority in the state in which the aircraft is registe ...

condition; it was exchanged in 2000 by the

Canadian Museum of Flight The Canadian Museum of Flight (formally the Canadian Museum of Flight Association since 1998) is an aviation museum at the Langley Regional Airport in Langley, British Columbia, Canada. The museum has over 25 civilian and military jets, pisto ...

for unflyable HUP-2 ''128529'', which was subsequently traded again in 2002 to the Shearwater Aviation Museum and repainted as ''51-16621''. ;Under restoration or in storage ;;UH-25B (HUP-2) * 128598 - Stored at

New England Air Museum The New England Air Museum (NEAM) is an American aerospace museum located adjacent to Bradley International Airport in Windsor Locks, Connecticut. The museum consists of three display hangars with additional storage and restoration hangars. Its ...

Windsor Locks, Connecticut Windsor Locks is a New England town, town in Hartford County, Connecticut, United States. The town is part of the Capitol Planning Region, Connecticut, Capitol Planning Region. As of the 2020 United States Census, 2020 census, its population was ...

. * 130053 – Stored at

Quartzsite, Arizona Quartzsite is a town in La Paz County, Arizona, United States. According to the 2020 census, the population was 2,413. Interstate 10 runs directly through Quartzsite which is at the intersection of U.S. Route 95 and Arizona State Route 95 wi ...

. * 130063 - Stored at New England Air Museum in Windsor Locks, Connecticut. ;;UH-25C (HUP-3) * 147610 –

Yanks Air Museum The Yanks Air Museum is an aviation museum dedicated to exhibiting, preserving and restoring American aircraft and artifacts in order to show the evolution of American aviation, located at Chino Airport in Chino, California. History A pair of F ...

in Chino, California, in storage."Piasecki HUP Retriever/147610."
''aerialvisuals.ca'' Retrieved: 5 May 2016.

Specifications (HUP-2)

References

;Notes ;Bibliography * Bridgman, Leonard. ''Jane's All The World's Aircraft 1956–57''. New York: The McGraw-Hill Book Company, 1956. * Harding, Stephen. ''U.S. Army Aircraft Since 1947''. Shrewsbury, UK:Airlife, 1990. . * .

External links

HUP Retriever warbird at the 2002 Chino Air Show
{{USN helicopters United States military helicopters Tandem rotor helicopters 1950s United States military aircraft 1950s United States helicopters Piasecki Helicopter aircraft Single-engined piston helicopters Aircraft first flown in 1948