Editing Boeing Vertol CH-46 Sea Knight (section)

==Development==
===Origins===
During the 1940s and 1950s, American rotorcraft manufacturer [[Piasecki Helicopter]] emerged as a pioneering developer of [[Tandem rotors|tandem-rotor]] helicopters; perhaps the most famous of these being the piston-powered [[Piasecki H-21|H-21]] "Flying Banana", an early utility and transport helicopter. During 1955, Piasecki was officially renamed as Vertol Corporation (standing for [[VTOL|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 T53]] turboshaft engines, each one being capable of producing 877 shp (640&nbsp;kW), commenced.<ref name=Apostolo>Apostolo, Giorgio. "Boeing Vertol Model 107". ''The Illustrated Encyclopedia of Helicopters''. New York: Bonanza Books. 1984. {{ISBN|978-0-517-43935-7}}.</ref>

[[File:Boeing Vertol 107 demonstratie, Bestanddeelnr 912-7031.jpg|thumb|right|V-107 prototype in 1961]]
On 22 April 1958, the V-107 prototype performed its [[maiden flight]].<ref name=Donald_V-107/> 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''.<ref name="whirly">Spenser, Jay P. ''Whirlybirds, A History of the U.S. Helicopter Pioneers''. University of Washington Press, 1998. {{ISBN|0-295-97699-3}} {{page needed|date=July 2019}}</ref> 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.<ref name="whirly"/> All of the U.S. Army's three YHC-1As were powered by pairs of [[General Electric T58|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''.<ref name="CH-46_hist_USN">[http://www.history.navy.mil/planes/ch46.htm CH-46 history page] {{webarchive |url=https://web.archive.org/web/20071203202119/http://www.history.navy.mil/planes/ch46.htm |date=3 December 2007}}. U.S. Navy, 16 November 2000.</ref>

During 1960, the [[United States Marine Corps|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.<ref name="vert_Tandom">"Tandem Twosome", ''Vertical Magazine'', February–March 2007.</ref> That same year, American aviation company [[Boeing]] acquired Vertol, after which the group was consequently renamed [[Boeing Helicopters|Boeing Vertol]].<ref name="whirly"/> 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''.<ref name="CH-46_hist_USN"/> During 1962, the [[United States Air Force|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 cancel 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.{{Citation needed|date=September 2022}}

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.<ref name="CH-46_hist_USN"/> The CH-46A was equipped with a pair of T58-GE8-8B turboshaft engines, each being rated at 1,250 shp (930&nbsp;kW); these allowed the Sea Knight to carry up to 17 passengers or a maximum of 4,000 pounds (1,815&nbsp;kg) of cargo.<ref name="vect_CH-46"/>

===Further developments===
[[File:HH-46D of HC-11 over USS Tripoli (LPH-10) in 1994.jpeg|thumb|left|HH-46D of the Navy resupplies {{USS|Tripoli|LPH-10|6}} during a [[Vertical replenishment|VERTREP]], 1994]]

During 1966, production of the improved ''CH-46D'' commenced with deliveries following shortly thereafter. This model featured various improvements, including modified [[rotor blade]]s and the adoption of more powerful T58-GE-10 turboshaft engines,<ref name="CH-46_hist_USN"/> rated at {{convert|1400|shp|kW|sigfig=3|abbr=on}} 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 {{convert|7000|lb|kg|sigfig=3}} of cargo.<ref name="vect_CH-46"/> During late 1967, the improved model was introduced to the [[Vietnam War|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.<ref>Rottman and Hook 2007, p. 10.</ref> Along with the USMC's CH-46Ds, the U.S. Navy also acquired a small number of UH-46Ds for ship resupply purposes.<ref name="Eden">Eden, Paul, ed. "Boeing-Vertol H-46 Sea Knight", ''Encyclopedia of Modern Military Aircraft''. Amber Books, 2004. {{ISBN|1-904687-84-9}}.</ref> In addition, approximately 33 CH-46As were progressively re-manufactured to the CH-46D standard.<ref name="vect_CH-46"/>

[[File:Marine Transport Squadron 1 150403-M-TW696-166.jpg|thumb|Formation of HH-46Es, used for search and rescue]]
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.<ref name="CH-46_hist_USN"/> 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 {{convert|1870|shp|kW|sigfig=3|abbr=on}} each; in addition, several CH-46Es were modified to double their maximum fuel capacity.<ref name="vect_CH-46"/> 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.{{Citation needed|date=April 2012}}

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.<ref name="vert_Tandom"/> During 1965, Boeing Vertol sold the manufacturing rights of the 107 to Japanese [[Conglomerate (company)|conglomerate]] [[Kawasaki Heavy Industries]]. Under this arrangement, all Model 107 civilian and military aircraft [[#Japanese versions|built in Japan]] were referred to by the ''KV 107'' designation.<ref name="vert_Tandom"/> On 15 December 2006, [[Columbia Helicopters, Inc]] acquired the [[type certificate]] for the BV 107-II, and with the help of Piasecki eventually developed an original design, the ''Model 107-III'', remanufactured from older airframes.<ref name="107-III">{{cite web |last1=Head |first1=Elan |title=Columbia and Piasecki partner on upgrade for 107-II and CH-46E helicopters |url=https://verticalmag.com/news/columbia-and-piasecki-partner-on-upgrade-for-107-ii-and-ch-46e-helicopters/ |website=Vertical Mag |date=4 July 2024 |access-date=21 January 2025 }}</ref>  This model features new manufactured CT58-GE-16 engines, the commercial version of the upgraded engines used for the CH-46E as well as modernized avionics including a glass cockpit.<ref name="107-III"/>