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Boeing Vertol CH-46 Sea Knight

Boeing · Medium-Lift Assault Transport / Vertical Replenishment · USA · Cold War (1970–1991)

Boeing Vertol CH-46 Sea Knight — Medium-Lift Assault Transport / Vertical Replenishment
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The Boeing Vertol CH-46 Sea Knight is an American twin-engine, tandem-rotor medium-lift helicopter built for U.S. Marine Corps and U.S. Navy operations. Developed by Boeing Vertol — originally Piasecki Helicopter, then Vertol Aircraft, and ultimately absorbed into Boeing — the type entered service in 1964, predating the 1970 cutoff used in this catalogue. The Sea Knight remained the Marine Corps' principal medium-lift assault helicopter for over 50 years, soldiering through the Cold War, post-Cold War, and War on Terror eras until U.S. Navy retirement in 2004 and Marine Corps retirement in 2014, when the V-22 Osprey took over the mission.

The airframe measures 84 ft (25.7 m) long with two 51-ft (15.5 m) main rotors fore and aft. Empty weight is 13,300 lb and maximum take-off weight is 24,300 lb. Power comes from two General Electric T58-GE-16 turboshafts rated at 1,870 shp each, later upgraded to T58-GE-100s in the CH-46E. Maximum speed is 165 mph (Mach 0.22), combat radius is 130 nmi typical, and service ceiling is 14,000 ft. The cabin accommodates 25 fully-equipped Marines, 15 stretchers plus medical attendants, or 7,000 lb of internal cargo with a 10,000 lb external sling load. The tandem-rotor layout eliminates the need to compensate for tail-rotor thrust, allows stable hover with side-to-side translation, and frees the entire fuselage length for cargo.

The Sea Knight's primary mission was Marine medium-lift assault — inserting and extracting Marines from amphibious-assault ships into ground operating areas. The U.S. Navy used the type for vertical replenishment between ships, and both services flew it on medical evacuation, combat search and rescue, and utility tasks. The Marine Corps received roughly 525 airframes, the Navy roughly 130, and foreign export operators included Canada (which flew the CH-113 Labrador variant), Sweden, and Saudi Arabia.

Marine CH-46s flew throughout the Vietnam War (1965-1973) as the principal medium-lift helicopter in theatre, and they delivered the iconic images of Operation Frequent Wind in April 1975 — the Saigon evacuation, with helicopters lifting evacuees from the U.S. Embassy roof. The type went on to serve in Operation Desert Storm (1991), Operation Iraqi Freedom (2003-2011), and Operation Enduring Freedom in Afghanistan (2001-2014). The Navy retired its UH-46s in 2004 once the MH-60S Seahawk took over vertical replenishment, and the Marine Corps followed in 2014 as the V-22 Osprey reached full fleet readiness. About 700 airframes were built in total, and around 75 survive in U.S. aviation museums.

For Kids — a shorter, friendlier version

The Boeing Vertol CH-46 Sea Knight is an unusual American helicopter. Instead of one big main rotor and a small tail rotor, it has two big rotors, one at each end of the helicopter body. The two rotors spin in opposite directions, balancing each other out. This design is called tandem rotor.

The Sea Knight has two General Electric T58 engines, each making 1,870 horsepower. It can fly at 165 mph, faster than a high-speed train, and carry 25 troops or 7,000 pounds of cargo. The big rotors at both ends let the Sea Knight lift heavy loads using the whole length of the helicopter, not just a single rotor in the middle.

The U.S. Marine Corps used Sea Knights to move troops, ammo, and supplies from ship to shore for over 50 years. CH-46 crews nicknamed it the 'Phrog' because of its frog-like shape. The Sea Knight flew in Vietnam, Iraq, Afghanistan, and many smaller conflicts and humanitarian missions.

About 524 CH-46 Sea Knights were built. The Marines retired their last ones in 2015, replaced by the much faster V-22 Osprey tiltrotor. A few CH-46 helicopters still fly today with the Department of State and private fire-fighting companies.

Fun Facts

  • The Sea Knight has two main rotors, one at each end, instead of the usual main-plus-tail layout.
  • Marines nicknamed it 'Phrog' (an old spelling of frog) because of its bumpy shape.
  • Both rotors spin in opposite directions, so no tail rotor is needed.
  • The CH-46 flew Marines from ship to shore for over 50 years.
  • About 524 CH-46s were built between 1962 and 1971.
  • The Marines retired their last CH-46s in 2015, replaced by V-22 Ospreys.
  • The CH-46 was originally designed by Vertol, then bought by Boeing in 1960.

Kids’ Questions

Why two rotors?

Most helicopters have one big rotor on top, plus a small tail rotor at the back to keep the helicopter from spinning. The CH-46 has two big rotors instead, one at each end. Each rotor spins the opposite way from the other, canceling out the spin. This design lets the CH-46 lift heavier loads and have no need for a tail rotor.

Why was it called 'Phrog'?

Marines who flew on the CH-46 noticed it had a humped, bumpy shape that looked a bit like a frog sitting on a lily pad. They started calling it 'Phrog' with a 'ph' to make it look different from the word 'frog'. The nickname stuck for the helicopter's entire 50+ year career.

What replaced it?

The Marines replaced the CH-46 Sea Knight with the V-22 Osprey, a tiltrotor that takes off like a helicopter and flies like an airplane. The V-22 is much faster (280 mph vs 165 mph) and can fly twice as far. The Osprey is more complicated and expensive, but it does the same job better than the old Phrog could.

Variants

CH-46A Sea Knight (initial USMC)
Original 1964 production variant with T58-GE-8 engines. Around 165 delivered to the U.S. Marine Corps and the backbone of Marine medium-lift through the early Vietnam War.
CH-46D Sea Knight (improved)
Improved 1966 variant with T58-GE-10 engines and updated systems. Around 85 delivered, used heavily in Vietnam.
CH-46E Sea Knight (mid-life)
Major mid-life upgrade with T58-GE-16 engines (later T58-GE-100), updated cockpit, and expanded mission systems. Around 280 delivered or converted from earlier marks. Carried Marine medium-lift through the 1980s, 1990s, and 2000s until the 2014 retirement.
UH-46 Sea Knight (USN utility)
U.S. Navy utility variant. Around 130 delivered for the vertical replenishment role, flown from supply ships until the 2004 retirement.
CH-113 Labrador (Canadian)
Canadian Forces variant. Around 12 delivered in 1964 and operated until 2003, when the Sikorsky CH-148 Cyclone took over.

Notable Operators

U.S. Marine Corps (former)
Primary operator. Around 525 CH-46s delivered between 1964 and 1971, flown by Marine Medium Helicopter Squadrons (HMM) including HMM-161, HMM-162, HMM-163, HMM-164, HMM-165, HMM-166, HMM-261, HMM-262, HMM-263, HMM-264, HMM-265, HMM-266, HMM-365, HMM-561, HMM-764, HMM-774 and Reserve units. Final retirement was with HMM-774 'Wild Goose' Reserve in October 2014.
U.S. Navy (former)
Around 130 UH-46s in service from 1965 to 2004 with Helicopter Combat Support Squadrons (HC) including HC-1, HC-3, HC-5, HC-6, HC-8, HC-11, and HC-16. Retired in 2004 as the MH-60S Seahawk took over vertical replenishment.
Canadian Forces (former, CH-113)
Around 12 CH-113 Labradors served from 1964 to 2003, flown principally on search and rescue and replaced by the Sikorsky CH-148 Cyclone.
Other foreign operators (former)
Sweden (around 5), Saudi Arabia (limited numbers), and a handful of other nations operated CH-46-derivative platforms. Most were retired by the 2010s.
Preservation / museums
Around 75 CH-46s are preserved across the United States. Public examples are held by the National Naval Aviation Museum (Pensacola, FL), the USS Midway Museum (San Diego), USS Yorktown / Patriots Point (Mount Pleasant, SC), and others.

Frequently Asked Questions

What is a tandem-rotor helicopter?

A tandem-rotor helicopter mounts two main rotors in line on the same fuselage — one forward, one aft — both providing lift, with no tail rotor required. Three benefits follow: stable hover and yaw without the side thrust of a tail rotor; an unobstructed full-length cargo cabin; and useful handling characteristics in certain flight regimes. The configuration is most closely associated with Boeing Vertol heritage, where the CH-46 Sea Knight and its larger sibling the CH-47 Chinook are the principal Western examples. Tandem-rotor operations continue today with the CH-47F Chinook and related platforms.

What replaced the CH-46?

For the U.S. Marine Corps, the V-22 Osprey tilt-rotor entered service in 2007 and progressively replaced the CH-46 from 2007 to 2014. For the U.S. Navy, the MH-60S Seahawk took over vertical replenishment, entering service in 2002 and replacing the UH-46 by 2004. The V-22's 277 mph cruise speed (against the CH-46's 165 mph) and 426 nmi combat radius (against 130 nmi) gave the Marine Corps a much longer reach, although unit cost and development time were both higher.

What was the CH-46's role in Vietnam?

It was the principal U.S. Marine Corps medium-lift helicopter throughout the Vietnam War (1965-1973). Marine CH-46s flew thousands of assault, casualty evacuation, and support missions, with around 109 airframes lost in combat. The type proved durable in jungle and mountain conditions. Operation Frequent Wind in April 1975 — the U.S. evacuation of Saigon — featured CH-46s lifting evacuees from the U.S. Embassy roof and other Saigon locations during the final hours of South Vietnam, producing some of the most recognised images of the war's end.

Why was CH-46 retired after 50 years?

Two reasons converged: airframe service-life expiration and the arrival of the V-22 Osprey. By the 2010s most CH-46E airframes were 40 to 50 years old, and component spares were increasingly hard to source after Boeing Vertol ended CH-46 production decades earlier. The V-22 programme — delayed by multiple fatal accidents during its 1990s development — entered Marine squadron service in 2007, allowing progressive CH-46 retirement from 2007 to 2014. The final Marine Corps retirement came in October 2014 with HMM-774 'Wild Goose' Reserve.

How does CH-46 differ from CH-47 Chinook?

Same tandem-rotor layout, different size class. The CH-47 Chinook is the U.S. Army heavy-lifter at 50,000 lb MTOW, 33+ troops, and 26,000 lb cargo. The CH-46 Sea Knight was the Marine medium-lifter at 24,300 lb MTOW, 25 Marines, and 7,000 lb internal plus 10,000 lb external cargo. Both are Boeing Vertol designs. The CH-47 remains in active service as the CH-47F Block II with planned upgrades through 2050 and beyond, while the CH-46 retired in 2014. Both have strong combat service records spanning decades.

Where can I see a CH-46 today?

Around 75 surviving CH-46s are preserved at U.S. aviation museums. Examples include the National Naval Aviation Museum (Pensacola, FL), the USS Midway Museum (San Diego, CA), USS Yorktown / Patriots Point (Mount Pleasant, SC), the USS Intrepid Museum (NYC), the Smithsonian National Air and Space Museum's Steven F. Udvar-Hazy Center, the Marine Corps Museum (Quantico, VA), and several state-level aviation museums. The type is well represented in U.S. naval-aviation collections, reflecting its 50-year service history.

Sources

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