Today, Navies across the world use an ingenious system to land helicopters
on the rolling deck of a ship at sea. It enabled the powerful helicopter-destroyer
combination that has become the dominant form of at sea anti-submarine warfare.
It's the “helicopter haul down and rapid securing device”, or more commonly known as Beartrap.
Experience with HMCS Labrador demonstrated that helicopters could be feasibility operated by
ships at sea. A flight deck and hangar were installed during construction and allowed
for the storage of its Piasecki HUP-3 and Bell HTL helicopters. Check out my video
about HMCS Labrador and her quest for the North-west passage for more information.
They flew from the deck when conditions allowed and the flight deck was comparable to one on land.
In the case of bad weather or high sea states the helicopters were grounded.
They had no effective way of securing the heavy helicopters to the deck nor moving them into the
hangar without significant human effort. While the Labrador proved helicopters could operate
from ships at sea, it also proved there was a need to develop a more effective and safer technique.
The Royal Canadian Navy was looking to expand its anti-submarine warfare capabilities
in the face of new, faster nuclear powered soviet submarines. Their destroyers weren’t
fast enough to guarantee an intercept and so ways of extending their reach were explored.
The RCN had two concurrent programs in place to address this, hydrofoils and helicopters.
The RCN had been involved with hydrofoil research since the second world war,
culminating in the incredible HMCS Bras D’Or. Super fast ocean going hydrofoils held
some promise but even before the Bras D’Or began trials it was on the chopping block.
Ultimately hydrofoils were abandoned in favor of using ship based helicopters.
Check out the video I made about the Bras D’Or for more details.
The next step was to try to actually land a helicopter on a destroyer sized ship at sea.
It was a bold move. Landing large helicopters on a small ship hadn’t been tried before.
Previously, helicopters were carried on aircraft carriers like HMCS Magnificent
and HMCS Bonaventure but the RCN wasn’t interested in operating a large fleet like that.
Instead they wanted to mate the efficiency of a destroyer with the capabilities of a
helicopter. This would help to reduce cost and increase flexibility as a fleet of many
helicopter-destroyer combos could patrol a greater stretch of ocean than one or two large carriers.
The Royal Canadian Navy’s VX 10 Experimental Squadron, based at Shearwater,
took on the job of developing a helicopter landing and handling system for ships.
They had worked on the Labrador starting in 1954 and learned many valuable lessons. Early RCN
helicopters like HUP-3s and HTVs were unsuitable for sustained anti-submarine warfare operations
but proved to be very useful in the arctic. Now the RCN was focused on
acquiring a more capable platform. This came in the shape of the Sikorsky HO4S-3.
These had dipping sonars and the legs to stay in the air for a meaningful amount of time.
Trouble was they were much larger and heavier than what they had previously worked with.
To gain further experience, a small flight deck was installed on the frigate, HMCS Buckingham.
Successful landings were made with an HO4S-3, mirroring the success on the
Labrador. A second flight deck was installed on the smaller destroyer escort HMCS Ottawa.
A larger Sikorsky S-58 was used in these tests and again proved to be successful.
This led to the conclusion that the destroyer-helicopter combo was a viable concept.
It was decided that the RCN’s new class of destroyer, called the St. Laurent-class,
would be modified to employ helicopters in an anti-submarine role as its primary weapons system.
However two things needed to be addressed. First off, the helicopters used in the tests lacked the
all-weather capabilities necessary for effective anti-submarine warfare operations. Secondly,
they needed a way to land and move a large helicopter on a pitching and rolling ship deck.
To answer the first need the RCN acquired the brand-new Sikorsky CH-124 Sea King. It
was much more capable than any type previously employed. It could operate in all-weather and
could carry systems to both track submarines and attack them. Check out my upcoming video
about the Sea King for more information about its long history with the RCN.
The Sea King is heavy with a gross weight of 8,449 kg (18,626 lb). This
made handling it on a moving flight deck almost impossible without some kind of aid. Landings
were comparatively easy as compared with trying to get the helicopter tucked into its hangar.
With the problem well defined, it was contracted out to Fairey Aviation in Dartmouth, Nova Scotia,
under the supervision of the RCN. What they came up with was called the
Helicopter Hauldown and Rapid Securing Device also known as the “Beartrap”.
The system was composed of several parts. A probe and cable assembly,
a control console, winch, power unit, anchor system, rails, and shock absorbers.
The first unit was installed on HMCS Assiniboine during her 1962-63 conversion which also saw
the addition of roll stabilizing fins, a landing pad, fueling facilities, and hangar.
How the whole system works is probably best explained by going over what a typical landing
looks like. To start the process, the landing helicopter will approach from the stern and match
the ship's forward speed, maintaining a hover just behind and to the left of the landing deck.
This allows the pilot to see the deck and begin radio communications with the landing control
officer onboard the ship. The pilot then lines up the ‘bum line’ marks on the deck.
They’re called bum lines because they line up their bums directly over them.
A small messenger probe is then lowered from underneath the helicopter. A crewman on board
the ship then grabs the probe, and connects it to the hauldown cable which comes out from the center
of the trap. The cables are then retracted into the helicopter and secured at its center of mass.
The pilot increases power as the winch operator pulls in the line to achieve ‘hover tension’.
This allows the helicopter to apply tension equal to its gross weight, making it much more stable.
The tension is maintained through a complicated system of winch controls and shock absorbers.
The cable is retracted by the LCO and the helicopter is brought down to the deck,
guiding its probe into the jaws of the trap. When it is safe,
the trap closes around the probe, securing the helicopter to the pitching and rolling deck.
A roll of 30 degrees and a pitch of 8 degrees can be easily managed by the system.
Once secured in the trap, a tail probe is connected and the engine powers down.
After this it's now safe to fold back the rotors and tail pylon
and move the helicopter across the flight deck and into the hangar.
Tracks on the deck allow the beartrap to be moved regardless of the ship’s motion.
Takeoffs were a bit less complicated. The helicopter is moved onto the flight deck
using the trap and rails. Once in position the engines are started and taken up to full idle.
The tail probe is retracted and the trap is released. The pilot then applies full
power and lifts off the deck when the LCO feels that there is a sufficient lull in
the motion of the ship. They then maintain a hover just above the deck to ensure that they
aren’t dragging any cables. Once given the all clear they pull away and begin their mission.
Daytime trials started in late 1963 and continued until mid-1964 using the new Sea Kings.
Nighttime and bad weather trials followed soon after and also proved successful.
The other 6 St. Laurent-class destroyers were equipped with their landing systems
and aviation facilities during their DDH refits. These were all completed by 1965.
By April 1967 the whole Beartrap system was fully up and running.
The system would later be installed on all newly
built Frigates and Destroyers serving in the Canadian fleet until the present day.
Other Navies were impressed with the Canadian achievement and wanted a similar system for
themselves. While their systems differed in some minor details and were built by different
manufactures, many other Navies including the US, the UK, Japan, and Australia were early
adopters of the Beartrap. Since then almost every Navy operating helicopters from small
ships use the basic Beartrap concept in some capacity. The exception being the harpoon and
grill approach but this lacks much of the function and safety of the Canadian system.
It really is the best way to solve the problem and so the solution was widely adopted.
In fact the Beartrap is so successful that it hasn’t seen
any major redesigns or changes since it was introduced over 60 years ago.
There have been advances made in how the probe is handled, or in some cases not handled, and how the
approach is performed and controlled, but the core probe and trap principle remains the same.
This device may be little known to the public, but it stands as one of the greatest contributions
Canada has ever made to naval aviation, and ushered in the age of helicopters at sea.