Development of the Sea Knight, which was originally designated by the firm as the Vertol Model 107, commenced during 1956. It was envisioned as a successor to the first generation of rotorcraft, such as the H-21 "Flying Banana", that had been powered by piston engines; in its place, the V-107 made use of the emergent turboshaft engine. On 22 April 1958, the V-107 prototype performed its maiden flight. During June 1958, the US Army awarded a contract for the construction of ten production-standard aircraft, designated as the YHC-1A, based on the V-107; this initial order was later cut down to three YHC-1As though. During 1961, the US Marine Corps (USMC), who had been studying its requirements for a medium-lift, twin-turbine cargo/troop assault helicopter, selected Boeing Vertol's Model 107M as the basis from which to manufacture a suitable rotorcraft to meet their needs. Known colloquially as the "Phrog" and formally as the "Sea Knight", it was operated across all US Marine Corps' operational environments between its introduction during the Vietnam War and its frontline retirement during 2014.
The Sea Knight was operated by the USMC to provide all-weather, day-or-night assault transport of combat troops, supplies and equipment until it was replaced by the MV-22 Osprey during the 2010s. The USMC also used the helicopter for combat support, search and rescue (SAR), casualty evacuation and Tactical Recovery of Aircraft and Personnel (TRAP). The Sea Knight also functioned as the US Navy's standard medium-lift utility helicopter prior to the type being phased out of service in favor of the MH-60S Knighthawk during the early 2000s. Several overseas operators acquired the rotorcraft as well. Canada operated the Sea Knight, designated as CH-113; the type was used predominantly in the search and rescue (SAR) role until 2004. Other export customers for the type included Japan, Sweden, and Saudi Arabia. The commercial version of the rotorcraft is the BV 107-II, commonly referred to simply as the "Vertol".
During the 1940s and 1950s, American rotorcraft manufacturer Piasecki Helicopter emerged as a pioneering developer of tandem-rotor helicopters; perhaps the most famous of these being the piston-powered H-21 "Flying Banana", an early utility and transport helicopter. During 1955, Piasecki was officially renamed as Vertol (standing for vertical take-off and landing); it was around this time that work commenced on the development of a new generation of tandem rotor helicopter. During 1956, the new design received the internal company designation of Vertol Model 107, or simply V-107; this rotorcraft differed from its predecessors by harnessing the newly developed turboshaft engine instead of piston-based counterparts. During that year, construction of a prototype, powered by a pair of Lycoming T53turboshaft engines, each one being capable of producing 877 shp (640 kW), commenced.
On 22 April 1958, the V-107 prototype performed its maiden flight. In order to garner publicity for the newly developed rotorcraft, it was decided to use the prototype to conduct a series of publicised flight demonstrations during a tour across the United States and several overseas nations. During June 1958, it was announced that the U.S. Army had awarded a contract to Vertol for the construction of ten production-standard aircraft based on the V-107, which were designated YHC-1A. However, this order was later decreased to three helicopters; according to aviation author Jay P. Spenser, the cutback had been enacted in order that the U.S. Army would be able to divert funds for the development of the rival V-114 helicopter, which was also a turbine-powered tandem rotor design but substantially larger than the V-107. All of the U.S. Army's three YHC-1As were powered by pairs of GE-T-58 engines. During August 1959, the first YHC-1A-model rotorcraft conducted its first flight; independently, it was shortly followed by the maiden flight of an improved model intended for the commercial and export markets, designated 107-II.
During 1960, the U.S. Marine Corps evolved a requirement for a medium-lift, twin-turbine troop/cargo assault helicopter to replace the various piston-engined types that were then in widespread use with the service. That same year, American aviation company Boeing acquired Vertol, after which the group was consequently renamed Boeing Vertol. Following a competition between several competing designs, during early 1961, it was announced that Boeing Vertol had been selected to manufacture its model 107M for the U.S. Marine Corps, where it was designated HRB-1. During 1962, the U.S. Air Force placed its own order for 12 XCH-46B Sea Knight helicopters, which used the XH-49A designation; however, the service later decided to cancelled the order due to delays in its delivery; instead, the U.S. Air Force opted to procure the rival Sikorsky S-61R in its place.
Following the Sea Knight's first flight in August 1962, the military designation was changed to CH-46A. During November 1964, the introduction of the Marines' CH-46A and the Navy's UH-46As commenced. The UH-46A variant was a modified version of the rotorcraft to perform the vertical replenishment mission. The CH-46A was equipped with a pair of T58-GE8-8B turboshaft engines, each being rated at 1,250 shp (930 kW); these allowed the Sea Knight to carry up to 17 passengers or a maximum of 4,000 pounds (1,815 kg) of cargo.
During 1966, production of the improved CH-46D commenced with deliveries following shortly thereafter. This model featured various improvements, including modified rotor blades and the adoption of more powerful T58-GE-10 turboshaft engines, rated at 1,400 shp (1,040 kW) each. The increased power of these new engines allowed the CH-46D to carry an increased payload, such as up to 25 troops or a maximum of 7,000 pounds (3,180 kg) of cargo. During late 1967, the improved model was introduced to the Vietnam theater, where it supplemented the U.S. Marine Corps' existing CH-46A fleet, which had proven to be relatively unreliable and problematic in service. Along with the USMC's CH-46Ds, the U.S. Navy also acquired a small number of UH-46Ds for ship resupply purposes. In addition, approximately 33 CH-46As were progressively re-manufactured to the CH-46D standard.
A door gunner manning a pintle-mounted .50-caliber M2 machine gun aboard a Marine CH-46, August 2006
Between 1968 and 1971, the U.S. Marine Corps received a number of CH-46F standard rotorcraft. This model retained the T58-GE-10 engines used on the CH-46D while featuring revised avionics and featured a number of other modifications. The CH-46F was the final production model of the type. During its service life, the Sea Knight received a variety of upgrades and modifications. Over time, the majority of the U.S. Marine Corps' Sea Knights were upgraded to the improved CH-46E standard. This model featured fiberglass rotor blades, reinforcement measures throughout the airframe, along with the refitting of further uprated T58-GE-16 engines, capable of producing 1,870 shp (1,390 kW) each; in addition, several CH-46Es were modified to double their maximum fuel capacity. Starting in the mid-1990s, the Dynamic Component Upgrade (DCU) programmes was enacted, focusing on the implementation of strengthened drive systems and modified rotor controls.
The commercial variant, the BV 107-II, was first ordered by New York Airways during 1960. During July 1962, they took delivery of their first three aircraft, which was configured to seat up to 25 passengers. During 1965, Boeing Vertol sold the manufacturing rights of the 107 to Japanese conglomerateKawasaki Heavy Industries. Under this arrangement, all Model 107 civilian and military aircraft built in Japan were referred to by the KV 107 designation. On 15 December 2006, Columbia Helicopters, Inc acquired the type certificate for the BV 107-II; at the time, the company was reportedly in the process of acquiring a Production Certificate from the Federal Aviation Administration (FAA). Plans for actual production of the aircraft were not announced.
A U.S. Marine watches two CH-46 Sea Knights, 2002
The Boeing Vertol CH-46 Sea Knight is a medium-lift tandem-rotortransport helicopter, furnished with a set of counter-rotating main rotors in a tandem-rotor configuration. It was typically powered by a pair of General Electric T58turboshaft engines, which were mounted on each side of the rear rotor pedestal; power to the forward rotor was transferred from the rear-mounted engines via a drive shaft. For redundancy, both engines are coupled so that either one would be capable of powering both of the main rotors in the event of a single engine failure or a similar emergency situation. Each of the rotors feature three blades, which can be folded to better facilitate storage and naval operations. The CH-46 features a fixed tricycle landing gear, complete with twin wheels on all three legs of the landing gear; this configuration results in a nose-up stance, helping to facilitate cargo loading and unloading. Two of the main landing gear were installed within protruding rear sponsons; the free interior space of the sponsons are also used to house fuel tanks, possessing a total capacity of 350 US gallons (1,438 L).
The interior of the CH-46 was largely taken up by its cargo bay, complete with a rear loading ramp that could be removed or left open in flight for the carriage of extended cargoes or for parachute drops. Various furnishings were normally provided to aid in its use as a utility rotorcraft, such as an internal winch mounted within the forward cabin, which can be used to assisting loading by pulling external cargo on pallets into the aircraft via the ramp and rollers, and an optionally-attached belly-mounted cargo hook, which would be usually rated at 10,000 lb (4,500 kg) for carrying cargoes externally underneath the Sea Knight; despite the hook having been rated at 10,000 lb (4,500 kg), this was safety restricted to less payload as they got older. When operated in a typical configuration, the CH-46 would usually be operated by a crew of three; a larger crew could be accommodated when required, which would be dependent upon mission specifics. For example, a search and rescue (SAR) variant would usually carry a crew of five (Pilot, Co-Pilot, Crew Chief, Swimmer, and Medic) to facilitate all aspects of such operations. For self-defense, a pintle-mounted 0.50 in (12.7 mm) Browningmachine gun could be mounted on each side of the helicopter. Service in southeast Asia resulted in the addition of armor along with the machine guns.
A flaming Marine CH-46 of HMM-265, after being hit by enemy AAA fire in "Helicopter Valley", 15 July 1966.
Known colloquially as the "Phrog", the Sea Knight was used in all U.S. Marine operational environments between its introduction during the Vietnam War and its frontline retirement in 2014. The type's longevity and reputation for reliability led to mantras such as "phrogs phorever" and "never trust a helicopter under 30". CH-46s transported personnel, evacuated wounded, supplied forward arming and refueling points (FARP), performed vertical replenishment, search and rescue, recovered downed aircraft and crews and other tasks.
During the Vietnam War, the CH-46 was one of the prime US troop transport helicopters in the theatre, slotting between the smaller Bell UH-1 Iroquois and larger Sikorsky CH-53 Sea Stallion. During the 1972 Easter Offensive, Sea Knights saw heavy use to convey US and South Vietnamese ground forces to and around the front lines. CH-46 operations were plagued by major technical problems; the engines, being prone to foreign object damage (FOD) from debris being ingested when hovering close to the ground and subsequently suffering a compressor stall, had a lifespan as low as 85 flight hours; on 21 July 1966, all CH-46s were grounded until more efficient filters had been fitted. By the end of US military operations in Vietnam, over a hundred Sea Knights had been lost to enemy fire.
In February 1968 the Marine Corps Development and Education Command obtained several CH-46s to perform herbicide dissemination tests using HIDAL (Helicopter, Insecticide Dispersal Apparatus, Liquid) systems; testing indicated the need for redesign and further study. Tandem-rotor helicopters were often used to transport nuclear warheads; the CH-46A was evaluated to deploy Naval Special Forces with the Special Atomic Demolition Munition (SADM). Nuclear Weapon Accident Exercise 1983 (NUWAX-83), simulating the crash of a Navy CH-46E carrying 3 nuclear warheads, was conducted at the Nevada Test Site on behalf of several federal agencies; the exercise, which used real radiological agents, was depicted in a Defense Nuclear Agency-produced documentary.
U.S. Marines load a simulated casualty onto a CH-46E during convoy operations training in May 2004.
CH-46E Sea Knights were also used by the U.S. Marine Corps during the 2003 invasion of Iraq. In one incident on 1 April 2003, Marine CH-46Es and CH-53Es carried U.S. Army Rangers and Special Operations troops on an extraction mission for captured Army Private Jessica Lynch from an Iraqi hospital. During the subsequent occupation of Iraq and counter-insurgency operations, the CH-46E was heavily used in the CASEVAC role, being required to maintain 24/7 availability regardless of conditions. According to authors Williamson Murray and Robert H Scales, the Sea Knight displayed serious reliability and maintenance problems during its deployment to Iraq, as well as "limited lift capabilities". Following the loss of numerous US helicopters in the Iraqi theatre, the Marines opted to equip their CH-46s with more advanced anti-missile countermeasures.
The U.S. Navy retired the type on 24 September 2004, replacing it with the MH-60S Seahawk; the Marine Corps maintained its fleet as the MV-22 Osprey was fielded. In March 2006 Marine Medium Helicopter Squadron 263 (HMM-263) was deactivated and redesignated VMM-263 to serve as the first MV-22 squadron. The replacement process continued through the other medium helicopter squadrons into 2014. On 5 October 2014, the Sea Knight performed its final service flight with the U.S. Marine Corps at Marine Corps Air Station Miramar. HMM-364 was the last squadron to use it outside the United States, landing it aboard USS America on her maiden transit. On 9 April 2015, the CH-46 was retired by the Marine Medium Helicopter Training Squadron 164, the last Marine Corps squadron to transition to the MV-22. The USMC retired the CH-46 on 1 August 2015 in a ceremony at the Udvar-Hazy Center near Washington DC. The HH-46E variant continued to operate in a Search and Rescue capacity at Marine Corps Air Station Cherry Point. The last flight of a Marine Corps H-46 took place on 25 September 2015 at MCAS Cherry Point and ended the 57-year Cherry Point Search and Rescue program.
The Royal Canadian Air Force procured six CH-113 Labrador helicopters for the SAR role and the Canadian Army acquired 12 of the similar CH-113A Voyageur for the medium-lift transport role. The RCAF Labradors were delivered first with the first one entering service on 11 October 1963. When the larger CH-147 Chinook was procured by the Canadian Forces in the mid-1970s, the Voyageur fleet was converted to Labrador specifications to undertake SAR missions. The refurbished Voyageurs were re-designated as CH-113A Labradors, thus a total of 15 Labradors were ultimately in service.
The Labrador was fitted with a watertight hull for marine landings, a 5,000 kilogram cargo hook and an external rescue hoist mounted over the right front door. It featured a 1,110 kilometer flying range, emergency medical equipment and an 18-person passenger capacity. By the 1990s, heavy use and hostile weather conditions had taken their toll on the Labrador fleet, resulting in increasing maintenance costs and the need for prompt replacement. In 1981, a mid-life upgrade of the fleet was carried out by Boeing Canada in Arnprior, Ontario. Known as the SAR-CUP (Search and Rescue Capability Upgrade Program), the refit scheme included new instrumentation, a nose-mounted weather radar, a tail-mounted auxiliary power unit, a new high-speed rescue hoist mounted over the side door and front-mounted searchlights. A total of six CH-113s and five CH-113As were upgraded with the last delivered in 1984.
In 1992, it was announced that the Labradors were to be replaced by 15 new helicopters, a variant of the AgustaWestland EH101, designated CH-149 Chimo. The order was subsequently cancelled by the Jean ChrétienLiberal government in 1993, resulting in cancellation penalties, as well as extending the service life of the Labrador fleet. However, in 1998, a CH-113 from CFB Greenwood crashed on Quebec's Gaspé Peninsula while returning from a SAR mission, resulting in the deaths of all crewmembers on board. The crash placed pressure upon the government to procure a replacement, thus an order was placed with the manufacturers of the EH101 for 15 aircraft to perform the search-and-rescue mission, designated CH-149 Cormorant. CH-149 deliveries began in 2003, allowing the last CH-113 to be retired in 2004. In October 2005 Columbia Helicopters of Aurora, Oregon purchased eight of the retired CH-113 Labradors to add to their fleet of 15 Vertol 107-II helicopters.
In 1963, Sweden procured ten UH-46Bs from the US as a transport and anti-submarine helicopter for the Swedish armed forces, designated Hkp 4A. In 1973, a further eight Kawasaki-built KV-107s, which were accordingly designated Hkp 4B, were acquired to replace the older Piasecki H-21. During the Cold War, the fleet's primary missions were anti-submarine warfare and troop transportation, they were also frequently employed in the search and rescue role. In the 1980s, the Hkp 4A was phased out, having been replaced by the Eurocopter AS332 Super Puma; the later Kawasaki-built Sea Knights continued in operational service until 2011, they were replaced by the UH-60 Black Hawk & NH90.
Columbia Helicopters BV 107-II in Papua New Guinea.
In December 2006, Columbia Helicopters purchased the type certificate of the Model 107 from Boeing, with the aim of eventually producing new-build aircraft themselves.
Company model number for basic prototype, one built.
Commercial airline helicopter. All subsequent commercial aircraft were produced as BV 107-II-2, two built as Boeing Vertol prototypes, five sold to New York Airways, ten supplied to Kawasaki as sub-assemblies or as parts. The second prototype was later rebuilt into a Sea Knight replacement for a lost unit in the Swedish navy she was named Y64 in Swedish service.
Medium-lift assault and cargo transport and SAR helicopter for the USMC, fitted with two 1,250 shp (935 kW) General Electric T58-GE-8 turboshaft engines. Previously designated HRB-1. 160 built for USMC, one static airframe.
Medium-lift utility transport helicopter for the United States Navy. Similar to the CH-46A. 14 built.
Approximately 50 CH-46As were converted into SAR helicopters for the United States Navy base rescue role.
Planned conversion of CH-46As into minesweeping helicopters for the US Navy, none converted. Nine SH-3As were converted to the RH-3A configuration instead.
Development of the CH-46A to specification HX/H2 for the United States Air Force; 12 ordered in 1962, cancelled and Sikorsky S-61R / CH-3C ordered instead.
YHC-1A redesignated in 1962. United States Army retained two, NASA used one for vertical autonomous landing trials (VALT).
Medium-lift assault and cargo transport helicopter for the USMC, fitted with two 1,400 shp (1,044 kW) General Electric T58-GE-10 turboshaft engines. 266 built.
Surviving HH-46A were upgraded and a small number of UH-46Ds were converted into SAR helicopters. SAR upgrades included the addition of an external rescue hoist near the front crew door and an 18-inch X 18-inch Doppler RADAR system located behind the nose landing gear, which provided for automatic, day/night, over-water hovering capability for at sea rescue. Additionally a "Loud Hailer" was installed opposite the crew entrance door for communicating with downed aviators on the ground or in the water.
Three CH-46Es were converted into SAR helicopters for Marine Transport Squadron One (VMR-1) at MCAS Cherry Point.
Improved version of CH-46D, electrical distribution, com/nav update BUNO 154845-157726. Last production model in the United States. 174 built, later reverted to CH-46E.
Unofficial designation of standard CH-46F used by HMX-1 as VIP support transport helicopter.
Replacement helicopter based on the Boeing Model 360, this Advance Technology Demonstrator from the 1980s never entered production. The aircraft relied heavily on composites for its construction and had a beefier drive train to handle the twin Avco-Lycoming AL5512 engines (4,200 shp).
On 15 July 1966 during Operation Hastings, two CH-46As BuNo 151930 and BuNo 151936 of HMM-164 collided at Landing Zone Crow while another, BuNo 151961, crashed into a tree avoiding the first two, resulting in 2 Marines killed. Another CH-46 BuNo 152500 of HMM-265 was shot down at the LZ later that day resulting in 13 Marines killed.
On 10 May 1996, a CH-46E collided in mid-air with an AH-1W, killing a combined fourteen troops (twelve Marines, one Navy sailor, and one Army soldier) aboard the two helicopters. The pilots of the CH-46E were injured. Both helicopters, of HMM-266, were operating from USS Saipan and were participating in Operation Purple Star, a joint exercise involving troops from the U.S. and the UK at Camp Lejeune, North Carolina.
On 9 December 1999, a CH-46D Sea Knight BuNo 154790 of HMM-166 crashed during a boarding exercise off the coast of San Diego, California, killing seven U.S. Marines. The pilot landed the CH-46 short on the deck of the USNS Pecos, causing the left rear tire and strut to become entangled in the safety netting at the back of the ship, which caused it to plunge into the ocean.
157688 – Classic Rotors Rotorcraft Museum in Ramona, CA. displays HH-46E '02' from VMR-1 Cherry Point MCAS N.C.
Data from The International Directory of Military Aircraft, 2002/2003, The Complete Encyclopedia of World Aircraft : Boeing Vertol Model 107 (H-46 Sea Knight), Encyclopedia of world military aircraft : Volume One
Crew: 5: two pilots, one crew chief, one aerial gunner/observer, one tail gunner
24 troops or
15 stretchers and two attendants or
7,000 lb (3,200 kg)
Length: 44 ft 10 in (13.67 m) (fuselage)
83 ft 4 in (25.40 m) (rotors turning)
Height: 16 ft 9 in (5.11 m) to top of rear rotor head
^Darrow, Robert A. (September 1971). Historical, Logistical, Political and Technical Aspects of the Herbicide/Defoliant Program, 1967–1971. Fort Detrick, Frederick MD: Plant Sciences Laboratories, US Army Chemical Corps. p. 30. A Resume of the Activities of the Subcommittee on Defoliation/Anticrop Systems (Vegetation Control Subcommittee) for the Joint Technical Coordinating Group/Chemical-Biological.
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