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Bet You Didn’t Know These 5 Things About the Sea Knight

Phrog, Sea Knight…Whatever you call it, the Trusty Helo that served our armed forces for over 50 years.

On April 22nd 1958 the prototype Vertol Model 107 flew for the first time. The 107 was a development of the Piasecki H-21 and the fifth tandem-rotor helicopter design by the engineers at Piasecki . Piasecki became Vertol in 1955. Vertol was then acquired by Boeing in 1960 and the company became Boeing Vertol. The Model 107 became the CH-46 Sea Knight. The Sea Knight, or Phrog, went on to serve with the United States Navy (USN) for 40 years and with the United States Marine Corps (USMC) for 51 years.

The design particulars for the CH-46 are that it was a twin-engine, tandem three-bladed folding rotor design powered by General Electric T-58 turboshaft engines. The machine mounted the engines in the tail and utilized a drive shaft to power the forward rotor. The engines were coupled in order to ensure that either could power the rotorcraft in an engine-out scenario. On the ground the CH-46 sat nose-high making the rear cargo ramp more accessible. Famous for their goofy looking grinning faces, and their rugged and capable character, the Phrogs worked hard to earn the respect bestowed upon them.

In June of 1958, the United States Army awarded a contract to Vertol for ten production aircraft to be designated YHC-1A. The Army then reduced the order quantity so they could spend their money on the larger but similar Model 114. Today you know the Vertol Model 114 as the venerable CH-47 Chinook. When the USMC decided to replace its piston-engine CH-34 Seahorse helos with a turbine powered rotorcraft in 1960 the CH-46 was the logical answer. Even the United State Air Force (USAF) took a look at the 107, but decided to go with the Sikorsky S-61R instead, which eventually became the CH-3C and later the HH-3E Jolly Green Giant in JUSAF service.

The designation of the production Sea Knight was changed from HRB-1to CH-46A when the Bureau of Aeronautics changed every aircraft designation in 1962. The CH-46A first flew later that same year. Deliveries of the Marine CH-46A and the Navy UH-46A, used primarily for shipboard vertical replenishment, began in November of 1964. Both models were capable of carrying up to 17 passengers or two tons of cargo. CH-46s were used to transport personnel and all manner of cargo, evacuate wounded, supply forward arming and refueling points, perform vertical replenishment, search and rescue, recover downed aircraft and crews, and whatever other jobs required a rotorcraft with a little extra pull.

The first Sea Knights to see combat were Marine CH-46As of Marine Medium Helicopter Squadron 164 (HMM-164) Knight Riders who arrived in Southeast Asia in early 1966. The improved CH-46D became operational later in 1966. Equipped with uprated engines driving better rotors, the CH-46D could carry up to 25 troops or three and a half tons of cargo (or a ton slung underneath). The USMC took the CH-46D into combat in Vietnam beginning late in 1967. Some 34 CH-46As were reworked to bring them up to CH-46D standards. The Navy also acquired UH-46Ds to replace their A models. Sea Knight production ended in 1971 after 524 airframes had been produced.

In Vietnam the Battle Phrog was the ultimate medium lift machine. Its capacity placed it between the smaller Bell UH-1 Iroquois and the larger Sikorsky CH-53 Sea Stallion. Always a prime mover of troops, the CH-46 experienced peak utilization during the 1972 Easter Offensive. CH-46s experienced their share of mechanical problems early on though. Like all turbine helicopter engines, foreign object damage (FOD) was a constant problem that required resolution. All in-country Battle Phrogs were grounded on July 21st 1966 until more effective intake filters were installed. The CH-46Ds were later grounded when a serious structural problem in the aft fuselage required “Iron Tail” fixes to the Battle Phrogs under the Sigma 1 program. Along the way the Battle Phrogs gained some weight by adding armor and door-mounted .50 caliber machine guns. Because of the inherent risk involved when operating rotorcraft in combat, 106 Marine Sea Knights were lost to enemy fire in Vietnam.

After Vietnam the Sea Knights were kept busy flying transport and replenishment hops. Many HH-46As and later HH-46Ds wore international orange accents as the primary base search and rescue helos at Naval Air Stations (NASs) and Marine Corps Air Stations (MCASs) around the world. Several examples were flown out of NAS Pensacola in the Florida panhandle supporting the various training commands housed at the sprawling complex. In 1983 when Operation Urgent Fury kicked off in Grenada, USMC Battle Phrogs flew the 8th Marine Regiment to the island and then did whatever work came up next. They rescued a downed helicopter crew, evacuated med school students, and moved Army Rangers and Force Recon Marines around the embattled tropical island. All in a day’s work for the Battle Phrogs.

The Marines used their CH-46Es during Operation Iraqi Freedom as well. On April 1st 2003, USMC CH-46E Sea Knights and CH-53E Super Stallions carried Special Operations troops and Army Rangers on their mission to extract captured US Army Private Jessica Lynch from an Iraqi hospital. During the occupation of Iraq and the counter-insurgency operations that followed, CH-46Es were utilized for the casualty evacuation (CASEVAC) role. CASEVASC-tasked helos are required to maintain 100% availability regardless of conditions, which tasked the by-then aging Battle Phrogs hard. The USMC decided to improve the anti-missile countermeasures of their Battle Phrogs after seeing losses reach unacceptable levels by adding chaff and flare dispensers and infrared (IR) detection and suppression equipment.

Even though no new CH-46s were built after 1971 the fleet Phrogs were continually improved and upgraded as they soldiered on. Many of the CH-46F variants received glass cockpits, stronger drive trains, fiberglass rotor blades, electrical and hydraulic system improvements, and further uprated T-58 engines. Crashworthiness and survivability were improved by changes to the fuel systems and the seating. To add more firepower a third .50 caliber machine gun mount was installed in the aft fuselage. The CH-46E (yes…not G…E) became an all-weather, day/night helicopter when avionics were upgraded. Upgrades continued through the 1980s and into the 1990s. The original heavier armor was replaced by lightweight protection and the motors were upgraded again, simplifying maintenance. Ironically, by the time it was finally time to retire the Phrogs they were the best rotorcraft they had ever been.

Navy Sea Knights were replaced by new technology in the form of the Sikorsky MH-60S Seahawk. The Navy retirement party for the CH-46 took place on September 24th 2004. The Marines continued to operate their Phrogs while the Bell-Boeing MV-22 Ospreys were being sorted out and coming online. Between 2006 and 2014 MV-22s steadily and inevitably replaced Marine CH-46s until the last operational USMC Battle Phrog flight at MCAS Miramar on October 5th 2014. The CH-46 Sea Knight was retired from operational use by Marine Medium Helicopter Training Squadron 164 (HMMT-164) on April 9th 2015. The USMC officially retired the Phrog on August 1st 2015 during a ceremony at the Smithsonian National Air and Space Museum’s Udvar-Hazy Center. There were 102 Phrogs in storage at AMARG at the time this article was written.

A civilian/commercial version of the 107 (the 107-II) went into service with New York Airways in 1962. Kawasaki Heavy Industries in Japan obtained 107 manufacturing rights in 1965 and dubbed their version the KV107. They are still building the KV107. Current and former military operators of the CH-46 series include Canada, Japan, Saudi Arabia, Sweden, Thailand, and the United States. Current and former civil operators of the 107 include Canada’s Helifor as well as Columbia Helicopters, New York Airways, Pan American Helicopters, and the Department of State in the United States.

Five things you might not know about the Sea Knight:

1. The “Dilbert Dunker” has been featured in movies such as Officer and a Gentleman (1982), but there is a second dunker waiting for aircrew and selected trainees at several NAS and MCAS locations that is in some ways more difficult to negotiate. The “Helo Dunker” is built to simulate the crash of a helicopter at sea. In operation it is dropped into a pool and then rotates to mimic the weight of the helicopter’s engines turning the fuselage inverted as it sinks. Students are required to process several tasks before egressing the trainer- along with several other students dunked simultaneously. The first couple of dunks are tough enough…but when they blindfold everybody (to simulate a night crash) it gets real interesting! Oh and they didn’t give us “egress bottles” back in the day either.

2. Phrogs have been featured in several movies over the years. In the James Bond film You Only Live Twice (1967) a KV-107 lifts a pesky S.P.E.C.T.R.E. car chasing our hero Bond and drops it into a conveniently-placed body of hard-as-concrete-from-that-height water. In Under Siege (1992) the bad guys get aboard the battleship Missouri via a Sea Knight. In Battle: Los Angeles (2011) Rules of Engagement (2000), and Heartbreak Ridge (1986) Marine Phrogs play supporting roles as well.
3. Marine CH-46s carried the last Marines off the United States Embassy rooftop in Saigon on April 30th 1975.
4. The Marine Helicopter Squadron that took the first Sea Knights into combat in Vietnam (HMM-164) was also the squadron who retired the Sea Knight 51 years later.
5. The popular military aviation saying “never trust a helicopter under 30” was attributed to the Marines who flew Battle Phrogs…not a single one of which was a day under 40 when they began to be replaced by the complicated and expensive MV-22.

One Comment

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  1. Good article, it makes me long for the old days.
    CH-46 Crew Chief/HMM-264/’80-’84

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Written by Bill Walton

Bill Walton

Bill Walton is a life-long aviation enthusiast and expert in aircraft recognition. As a teenager Bill helped his engineer father build an award-winning T-18 homebuilt airplane in their Wisconsin basement. Bill is a freelance writer, an avid sailor, engineer, announcer, husband, father, uncle, mentor, coach, and Navy veteran. Bill lives north of Houston TX with his wife and son under the approach path to KDWH runway 17R, which means they get to look up at a lot of airplanes. A very good thing.

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