Boeing Vertol CH-46 Sea Knight

Updated: October 2026 – Two rotors turn one behind the other, the nose perks up, and the whole thing looks a bit like a shrunken Chinook: then you very likely have a Boeing Vertol CH-46 Sea Knight in front of you. For about half a century it was the workhorse of the US Marines, plus sea rescuer in Canada and submarine hunter in Sweden. Today it is retired almost everywhere. On this page you will learn how to identify it with certainty, how it differs from the Chinook, what became of the civil version, the Model 107, and where you can still see one.

What is the CH-46 Sea Knight?

The CH-46 is a medium transport helicopter with two rotors in tandem arrangement and two shaft turbines. It goes back to the Vertol Model 107, which first took off on April 22, 1958. Vertol – which emerged from the helicopter pioneer Piasecki – was taken over by Boeing in 1960 and traded afterward as Boeing Vertol. The larger CH-47 Chinook, still built today, also comes from this line.

The tandem principle has a big advantage: because the two rotors turn in opposite directions, their torques cancel each other out. A tail rotor is unnecessary, and all of the engine power goes into lift. The design also tolerates a wide center-of-gravity range – handy for a helicopter that hauls troops one day, litters the next and pallets the one after.

The US Army first tested a version as the YHC-1A but then decided on the larger Chinook. The US Marine Corps, by contrast, chose an adapted variant in 1961 as its new troop transport. After the first flight in August 1962 it received the designation CH-46A, and from November 1964 it entered operational service. By 1971 a total of 524 aircraft of the H-46 series were built; civil Model 107s and the Japanese licensed production come on top of that.

Design in brief

The two GE T58 turbines sit left and right on the rear rotor pylon. A shaft carries the power forward to the front rotor; if one engine fails, the other can drive both rotors. The rotor blades can be folded so that the helicopter fits into tight hangars on ships.

The landing gear is fixed and has dual wheels on all three legs. The main gear sits in short stubs on the fuselage sides, which also hold fuel. Because the nose wheel stands higher, the Sea Knight raises its nose on the ground – that makes loading over the rear ramp easier. The underside of the fuselage is watertight, so that the helicopter can land on the water in calm seas and float for a limited time.

The three features that are enough for identification

There are not many tandem-rotor helicopters. When you see such a silhouette, you can narrow it down reliably with three observations.

These three points are enough in practice. In the end, the serial number or registration confirms the type and often the exact variant. How to read US military serial numbers is explained in the article on US military serials.

The variants at a glance

Over the decades the Sea Knight was modernized several times. For spotters, the versions are often hard to tell apart from the outside; serial number and unit help.

Variant	Operator	Special feature
CH-46A	US Marine Corps	First production version with T58-GE-8
UH-46A / UH-46D	US Navy	Resupplying ships from the air (vertical replenishment)
CH-46D	US Marine Corps	More powerful T58-GE-10, 266 built
CH-46F	US Marine Corps	Last new-build version with revised avionics
CH-46E	US Marine Corps	Service life extension with fiberglass rotor blades and T58-GE-16, the most important late version
HH-46A / HH-46D / HH-46E	US Navy, USMC	Search and rescue versions, HH-46D with rescue hoist and Doppler radar
CH-113 / CH-113A	Canada	Labrador (sea rescue) and Voyageur (Army transport)
Hkp 4	Sweden	Air Force and Navy, sea rescue and anti-submarine warfare
KV-107	Japan, Saudi Arabia, etc.	Licensed production by Kawasaki from 1965
BV 107-II	civil operators	Civil base model, including New York Airways and Pan Am

Operational history with the US Marines

In Vietnam the CH-46 became the Marines’ most important troop transport. It closed the gap between the small UH-1 “Huey” and the heavy CH-53. The first years were hard: the engines sucked in dirt while hovering over dusty landing zones, and in 1966 and 1967 the type had to stay grounded several times because of technical problems. Investigations found structural weaknesses at the rear pylon, which were then fixed. By the end of US operations, more than 100 Sea Knights had been lost to enemy fire in Vietnam.

The Sea Knight has a permanent place in the history books through the evacuation of Saigon in April 1975: the last helicopter to lift off from the roof of the US Embassy was a CH-46. After that the type flew, among other things, in the landing on Grenada in 1983, in Iraq from 2003 and in Afghanistan.

From 2006 the transition to the tiltrotor MV-22 Osprey began. The first squadron, HMM-263, was renamed VMM-263. A CH-46 made the last service flight on October 5, 2014 at Marine Corps Air Station Miramar; the last training squadron gave up the type in April 2015. The official farewell ceremony took place on August 1, 2015, at the Steven F. Udvar-Hazy Center near Washington.

Even after the farewell with the Marines, the type had not quite disappeared: from 2011, retired CH-46Es were refurbished for the US State Department’s air fleet and used, among other places, in Afghanistan. During the withdrawal from Kabul in August 2021, several of these aircraft were left behind at the airport, disabled.

The Sea Knight in Sweden: Hkp 4

For European spotters, the Swedish story is the most exciting. From 1963, Sweden received the first aircraft; in all there were 22 examples – partly from Boeing Vertol, partly from Japanese Kawasaki production. The Swedish armed forces operated them as the Helikopter 4 (Hkp 4) in several sub-variants.

• Air Force (Flygvapnet): The Hkp 4As served mainly search and rescue readiness at various air wings. They were replaced by the Super Puma, the Hkp 10 in Sweden.
• Navy (Marinflyget): Here the Hkp 4 hunted submarines with dipping sonar, depth charges or torpedoes – a task that was very real in the Swedish archipelago during the Cold War.
• Civil emergencies: The helicopters helped with the fire on the ferry Scandinavian Star in 1990, the sinking of the Estonia in September 1994 and in fighting forest fires.

From 1998, the remaining aircraft flew in the newly formed helicopter wing, increasingly as transport helicopters. The last flight for the Swedish armed forces took place on March 1, 2011. The NH90 (Hkp 14) had actually been intended as the successor for anti-submarine warfare, but its introduction was delayed; for medevac flights, Sweden procured UH-60M Black Hawks (Hkp 16) at short notice in 2011 – more on the type on the page about the Sikorsky UH-60 Black Hawk. Most of the remaining Hkp 4s went to Columbia Helicopters in the USA in 2012.

Canada, Japan and other operators

In Canada the type flew as the CH-113 Labrador with the Air Force in sea rescue; the first aircraft entered service in October 1963. The Army received the transport version CH-113A Voyageur, which after the introduction of the Chinook was also converted into rescue helicopters. The last Labrador left service in 2004, and the successor was the CH-149 Cormorant – a version of the AW101.

Japan acquired the license in 1965; Kawasaki built the type as the KV-107 for the air, ground and maritime forces and the Tokyo police. Kawasaki aircraft also went into export, for example to the Saudi Arabian Interior Ministry for firefighting, rescue and medical transport and to the Thai Army. The Swedish Hkp 4s of the later deliveries also come from Kawasaki production.

Argentina wrote a curious chapter: in September 2023 the country asked the USA for approval to refurbish stored CH-46s from Arizona to supply its Antarctic stations. How that goes on is open – if you are interested, check the current status.

Model 107: the civil side

Vertol had intended the Model 107 for the civil market from the start. New York Airways ordered the passenger version BV 107-II in 1960 and took over the first aircraft in July 1962. The airline used it to fly feeder service between the New York airports and Manhattan. Pan Am also used the 107 in the mid-1960s, among other things for flights from the roof of the Pan Am Building in Manhattan to JFK Airport – today a piece of aviation nostalgia.

Later the 107-II found its niche in external-load work with specialist operators. In December 2006, Columbia Helicopters of Oregon took over the type certificate. The company bought used aircraft from Canada and Sweden, resold individual examples and in 2023 began refurbishing older 107-IIs and former CH-46Es; it also developed the concept of a modernized Model 107-III. For you as a spotter that means: anyone who still wants to catch a flying tandem rotor of this family looks most likely at civil specialist operators in North America.

Sea Knight, Chinook or Osprey?

The three types are often confused because they have similar tasks and often turn up together in photos from US military aviation. The finder helps you narrow it down.

If you want to feel more confident about rotorcraft in general, the guide Recognizing helicopter types helps. Another Marine classic with a boat hull, by the way, is the Westland Sea King – though it has only one main rotor plus a tail rotor.

Where to see the Sea Knight today

In European airspace the CH-46 has practically disappeared. Your best chances are in museums and – with luck – with civil operators in North America.

Place	What awaits you	Note
Flygvapenmuseum Linköping (Sweden)	Hkp 4 from Swedish service	Combines well with Saab classics
Aeroseum Gothenburg (Sweden)	Two Hkp 4s, one airworthy according to Swedish information	Check flight dates in advance
Pima Air & Space Museum Tucson (USA)	CH-46E in the outdoor area	Huge collection in the desert
Udvar-Hazy Center near Washington (USA)	Marine CH-46	Venue of the 2015 farewell ceremony
National Museum of the Marine Corps (USA)	Rear fuselage half of a CH-46D	Focus on Marine history
Columbia Helicopters (USA)	Civil 107-II in work service	Missions change, no fixed sighting places

The Pima Air & Space Museum in Tucson is worthwhile anyway for anyone who loves US military aviation; tips for photos on site are on the spot page for the Pima Air & Space Museum. If you are in Washington, combine the Udvar-Hazy Center at Dulles Airport with a spotting detour, and in Sweden the museum is right at Malmen airfield near Linköping. If you go rotorcraft hunting in Germany, you will find a good overview of the development of helicopter technology at the Bückeburg Helicopter Museum – whether a tandem rotor of the 107 family is there, you are best off checking with the museum beforehand.

Photo tips for tandem rotors

A Sea Knight is a rewarding subject – whether in a museum or, with a lot of luck, in the air.

How to photograph rotorcraft in general and where to find them in Germany is in the guide Spotting helicopters. If you want to follow military aircraft live, Tracking military aircraft online helps, and for looking up serial numbers and units, Scramble is worth a look. Before you photograph at an active military airfield, read the rules for photography at military airfields.

Common mix-ups and how to rule them out

Conclusion

The CH-46 Sea Knight is one of the great classics among military helicopters. Compact tandem rotor, three landing gear legs and the cheeky, raised nose make it unmistakable once you have consciously seen it. With the Marines, in Canada and in Sweden it is history; as the civil Model 107 it lives on with specialist operators. For spotters in Europe, the way to it today leads mainly through Swedish museums.