The Gannet grew directly out of the anti-submarine lessons of the Second World War, when German U-boats had come close to cutting Britain’s Atlantic lifeline. In 1945 the Admiralty issued Specification GR.17/45 for a new carrier aircraft that could carry out the whole anti-submarine mission in one airframe — searching for the submarine, and then attacking it — from the deck of an aircraft carrier.

Fairey Aviation’s design, initially known as the Type 17, first flew on 19 September 1949. Development took several years, as the novel Double Mamba engine and the aircraft’s complex systems were perfected, and the Gannet AS.1 finally entered Fleet Air Arm service in 1955. It was one of the first purpose-designed, turboprop-powered carrier anti-submarine aircraft in the world.

The Gannet’s defining feature was its powerplant, the Armstrong Siddeley Double Mamba (or “Twin Mamba”). It consisted of two Mamba turboprop engines mounted side by side and coupled through a common gearbox, each driving one of two contra-rotating propellers on the nose. In effect it was a single power unit made of two independent halves.

This gave the Gannet the best of both worlds. With both engines running it had ample power for a heavily loaded carrier takeoff and for climb and dash. And because the halves were independent, the aircraft did not depend on both to fly — a vital safety margin over the sea, and the key to its most useful trick.

The real payoff of the Double Mamba came on patrol. An anti-submarine aircraft earns its keep by staying airborne over a search area for as long as possible, and here the Gannet had a unique advantage: once it reached its patrol station, the crew could shut down one of the two engines and feather its propeller, cruising economically on a single Mamba.

Running on half its powerplant, the Gannet burned far less fuel and could loiter for hours longer than a conventional aircraft of similar size. The contra-rotating propellers made this practical — with one propeller stopped, there was no great asymmetric drag or torque to fight. It was a genuinely elegant piece of engineering, tailored precisely to the endurance the anti-submarine mission demanded.

The Gannet’s two propellers, mounted one behind the other on concentric shafts, turned in opposite directions. This contra-rotating arrangement absorbed the considerable power of the Double Mamba through a large total blade area while keeping the propeller diameter manageable for a carrier aircraft — important for deck clearance.

Just as valuable, contra-rotating propellers cancel out each other’s torque and slipstream effects. A single large propeller of that power would have tried to twist the aircraft on takeoff and made it a handful to fly; the balanced pair made the Gannet docile and predictable, exactly the qualities wanted for the demanding business of landing on a pitching carrier deck.

Space on an aircraft carrier is precious, and the Gannet was designed around it. Its wings folded — and not just once: the Gannet used a distinctive double-fold, each wing folding twice, to shrink the aircraft’s span dramatically so that more could be packed into the hangar below deck. Folded, the portly Gannet took on an ungainly, insect-like look that enthusiasts came to love.

Everything else about the aircraft was built for the deck too: a sturdy undercarriage and arrester hook for carrier landings, an internal weapons bay to keep the airframe clean, and three crew seated in tandem within the deep fuselage. It was never elegant, but it was superbly practical — a true carrier aircraft in every detail.

In its original role the Gannet was a submarine-hunter, and it carried the tools of the trade. A retractable radar under the rear fuselage searched for submarines caught on the surface; sonobuoys, dropped into the sea, listened for submerged boats; and an internal weapons bay held homing torpedoes and depth charges to attack. The two observers behind the pilot worked the sensors and directed the hunt.

The AS.1 entered service in 1955, followed by the more powerful AS.4. Flying from Britain’s carriers through the late 1950s and early 1960s, the Gannet was the Fleet Air Arm’s fixed-wing answer to the growing Soviet submarine threat — until the anti-submarine role began passing to helicopters, which could dip a sonar directly into the water and fly from far smaller ships.

The Gannet’s second career was as an airborne-early-warning aircraft. A fleet’s own ships can only see as far as their radar horizon, leaving them blind to low-flying aircraft and missiles until it is almost too late. The solution is to lift a radar high into the air, and Britain did exactly that by fitting the big American AN/APS-20 radar into a much-modified Gannet.

The result, the AEW.3, carried the radar in a large radome slung beneath the fuselage and entered service from 1960. Orbiting ahead of the fleet, it could detect threats far beyond the range of the ships’ own radars and vector fighters to intercept them. For nearly two decades the AEW.3 was the Royal Navy’s carrier-borne early-warning capability — an unglamorous but genuinely vital job.

The Gannet AEW.3 was tied to Britain’s large fleet carriers, and when the last of them, HMS Ark Royal, was decommissioned in 1978, the AEW.3 retired with her. The Royal Navy was left with no carrier-borne fixed-wing early-warning aircraft at all — a capability quietly lost as the fleet moved to smaller carriers operating Sea Harriers and helicopters.

The consequences became tragically clear in the 1982 Falklands War. Without airborne radar cover, the British task force could not reliably detect low-level Argentine air attacks in time, and several ships were hit and sunk. The Navy responded by rushing early-warning radars onto Sea King helicopters as a stopgap. The Gannet AEW.3’s retirement, and the gap it left, is one of the most-cited lessons of the campaign.

Beyond the anti-submarine and early-warning versions, the Gannet was adapted to other carrier tasks. The COD.4 — carrier onboard delivery — was a transport conversion used to ferry passengers, mail and urgent spare parts out to carriers at sea, a mundane but essential service. Electronic-countermeasures versions such as the ECM.6 supported the fleet’s electronic-warfare needs.

There were also dual-control trainer versions, the T.2 and T.5, used to convert aircrew onto the type. This spread of variants — from submarine-hunter to radar picket to carrier van to trainer — shows how thoroughly the Gannet’s roomy, practical airframe was worked into the fabric of Fleet Air Arm carrier operations.

Though designed for the Royal Navy, the Gannet found overseas customers. The Royal Australian Navy operated Gannets in the anti-submarine role, flying them from its aircraft carrier HMAS Melbourne through the late 1950s and 1960s. The West German Bundesmarine used land-based Gannets for maritime patrol over the Baltic and North Sea, and the Indonesian Navy also operated the type.

These export sales spread the Gannet’s distinctive shape and its clever Double Mamba engine well beyond Britain. Each operator used the aircraft for the same essential purpose — watching the sea and hunting submarines — and the Gannet’s presence in Australian, German and Indonesian service is a measure of how well it filled a role that many maritime nations needed filled.

As with most Cold War military aircraft, there is no single reliable, transparent public figure for the Gannet’s unit cost, cost per flight hour or total programme cost. It was procured in modest numbers over several years, in a range of variants, through government contracts rather than at a published list price, and consistent lifetime cost data for the type is not available. Any single figure quoted for it should be treated with caution.

What can be said is that the Gannet’s whole design philosophy — the one-engine loiter of the Double Mamba above all — was aimed at efficiency and endurance, getting the most patrol time from each hour of flying. Rather than invent numbers, we list the cost fields here as “not reliably recorded.”

The Gannet was an excellent fixed-wing submarine-hunter, but by the early 1960s the anti-submarine mission was shifting to helicopters, and for good reasons. A helicopter can hover motionless over a patch of sea and lower a “dipping” sonar directly into the water to listen for a submarine — something no fixed-wing aircraft can do. It can also operate from small escort ships, not just large carriers, spreading anti-submarine cover across the whole fleet.

As helicopters like the Westland Whirlwind and Wessex matured, they took over the close-in anti-submarine role from the Gannet. This freed the Gannet airframe for its second life as the AEW.3 radar picket — a job the helicopters of the day could not do — and so the aircraft’s career was extended rather than ended by the change.

The Gannet is a great favourite among aviation enthusiasts — distinctive, characterful and full of clever engineering — and thanks to that affection a good number survive. Museum examples are preserved in Britain, in Australia, in Germany and elsewhere, spanning the anti-submarine and airborne-early-warning versions, and for a number of years a few Gannets were even kept in flying condition on the airshow circuit.

These survivors keep alive the memory of one of the Cold War’s most ingenious carrier aircraft: the double engine that could run on half its power, the wings that folded twice, and the big-eyed AEW.3 that watched the horizon for the fleet. For an aircraft that never sought glamour, the Gannet has earned a devoted following.