It's a Plane . . . a Helicopter . . . a Phrog!

The iconic helicopter of the Korean War was the Bell H-13, which was featured in the television series M*A*S*H, and that of the Vietnam War was the Bell UH-1 “Huey,” shown in the film Apocalypse Now carrying a Navy PBR. But for the past half-century the iconic helicopter of the Marine Corps has been the CH-46 Sea Knight, generally referred to as the “phrog.”

The aircraft—based on earlier designs by helicopter pioneer Frank Piasecki—was developed in the late 1950s by Boeing Vertol with the company designation Model 107 for evaluation by the U.S. Army as a medium-lift transport helicopter.¹ That service ordered ten in 1958 as the YHC-1A. But only three were produced plus five modified, more powerful aircraft as the YHC-1B, later named Chinook and, in 1962, changed to CH-47A. 

The Marine Corps decided to procure the YHC-1A in quantity, becoming the HRB-1 in the  Navy’s designation scheme and being named Sea Knight; it was changed to CH-46A in 1962.² 

These helicopters featured tandem rotors to take advantage of small, lightweight turboshaft engines; also, that configuration alleviated the need for the traditional tailboom. Two General Electric T-58-8B engines drove the two contra-rotating, three-blade rotors. The original blades were of steel and aluminum with 275 Navy and Marine aircraft being refitted with fiberglass blades from 1980 onward. The rotor blades folded for shipboard stowage.

The engines were fitted above the rear fuselage to facilitate loading vehicles and troops directly into the cabin via a rear hydraulic ramp.³ The fuselage, which was watertight for emergency landings, had non-retractable tricycle landing gear. The main wheels protruded from small sponsons at the after end of the fuselage. (While generally similar to the CH-46, the CH-47 could easily be distinguished by its large, full-length sponsons and quadricycle landing gear.)

The long-delayed first flight of the CH-47A occurred on 16 October 1962. The helicopter was introduced into Marine squadrons as the HRB-1/CH-46A in 1962 and into Navy service as the HRB-1/UH-46A for at-sea replenishment operations in 1964. Thirty-four UH-46A/D models served in the vertical replenishment (VERTREP) role, later replaced by CH-46Ds. The Navy also acquired the HH-46A for air-sea rescue, that aircraft having Doppler radar, a hull modified for water landing, and a rescue hoist; one CH-46 was modified to an RH-46A for evaluation in the minesweeping configuration.

The CH-46A requirements were to carry 4,000 pounds of cargo or 17 fully equipped troops with a combat radius of 115 miles at a speed of 150 miles per hour.

Marine Medium Helicopter Squadron (HMM) 265 became the first to acquire the Sea Knight. But it was HMM-164 that first deployed to war, with 27 CH-46A helicopters arriving in South Vietnam in March 1966. The increased lift of the CH-46A compared with the earlier HUS/UH-34 Seahorse made it an important contribution to Marine capabilities, despite initial problems of excessive vibration and sand damage to the engines and rotor blades.⁴ The sand situation became so serious that engines were being replaced after 200 to 300 landings, and at times the aircraft were grounded except when heavy-lift capabilities were especially required or for emergencies. According to one officer engaged in managing the CH-46 program, “By the summer of 1967, major accidents and mechanical failures involving the CH-46 reached crisis proportions.”⁵ Filter kits were provided in the field, and helicopters were pulled from the war zone and returned to Boeing Vertol for a “major rebuilding of the airframe.”

The CH-46A had a “hover-aft” feature that provided a “technique” of dropping down to tree level and coming toward the landing zone at maximum speed. At the last second the pilot executed a hard turn to the zone and hit the hover-aft switch. The rear rotor then acted like a speed brake as the helicopter landed. 

Marines flew the helicopters through the end of the Vietnam conflict, rushing troops and munitions to critical battles, and evacuating the wounded. They suffered accordingly: 106 were shot down in combat, as were two Navy UH-46 VERTREP helicopters. At some stage during the war the Marines began calling them “phrogs,” undoubtedly an allusion to the green-painted CH-46 resembling a giant frog perched on its hind legs.

Improved versions of the H-46 were produced, with more powerful (and protected) turboshaft engines. The final production aircraft—a CH-46F—was rolled out of the Boeing Vertol plant in Morton, Pennsylvania, on 2 February 1971. The plant had built 624 A/D/F models for the Marines since 1962. Beyond the Marine Corps and Navy orders, Boeing Vertol produced 18 H-46 variants for Canada and 14 for Sweden. Only Sweden flew the aircraft in the antisubmarine role. Boeing Vertol had sought other customers for that mission, noting that the tandem rotors reduced downwash compared to single-rotor helicopters, thus reducing underwater noise to achieve better dipping-sonar performance.

The success of the H-46 was recognized when Kawasaki in Japan began producing the KV-107 helicopter for the Japan Self-Defense Forces: 9 for mine countermeasures, 59 troop carriers for ground forces, and 30 for air search-and-rescue; another 8 were built in Japan for Sweden and 6 for Saudi Arabia—four of the latter for the firefighting role. Many U.S.- and Japanese-built helicopters had “second careers” in other air services.

But the primary Sea Knight operator was the U.S. Marine Corps, with the CH-46 being flown from bases ashore and from amphibious ships in conflicts and crises ranging from the Caribbean to Afghanistan. Despite modernizations and updates, the Sea Knights eventually reached the end of their service lives. The last Marine CH-46E was retired on 1 August 2015, and the last Navy HH-46E on 29 September 2015. (In 2016 the State Department was flying Sea Knights in Afghanistan in support of its narcotics-suppression actions . . . all very “hush hush.”)