The Sunderland was born from luxury. In the 1930s Short Brothers built the Empire (C-Class) flying boats, graceful four-engine machines that carried mail and passengers in comfort along the air routes of the British Empire. Their large, efficient hull and wing were exactly what a long-range military flying boat needed.

When the Air Ministry called for a modern maritime-reconnaissance flying boat, Short developed the Sunderland from that civil design, militarising the hull, adding turrets and a bomb load, and strengthening the structure for war. It first flew in 1937 and entered RAF service in 1938. The civil pedigree gave the Sunderland its roomy, seaworthy hull and its comfortable interior — qualities that would prove unexpectedly valuable on the long patrols to come.

More than almost any other aircraft, the Sunderland was a genuine ship of the air. Its deep, boat-shaped hull had two decks, and the interior included a wardroom, a galley with a cooker for hot meals, bunks for off-watch crew, a workshop with tools and spares, and stowage for the anchor and mooring gear every flying boat needed. The crew even used nautical language, and the aircraft was moored, beached and handled like a vessel.

This was not indulgence. On patrols lasting well over half a day, the ability to feed and rest the ten-to-thirteen-man crew directly affected how well they did the job — a warm, rested lookout on the thirteenth hour was far more likely to spot the feather of a periscope than an exhausted, frozen one. The flying-ship interior was a practical answer to the brutal demands of very long over-water patrol.

The Sunderland’s nickname — the “Flying Porcupine”, or Stachelschwein, reportedly bestowed by Luftwaffe crews — came from its heavy defensive armament. Power-operated turrets in the nose and tail, plus guns in beam and dorsal positions, gave it a spiky, all-round sting that made attacking it a genuinely dangerous proposition for a fighter.

The reputation was earned in action. In one much-recounted engagement in 1940, a lone Sunderland attacked by a formation of Junkers Ju 88s fought back so effectively that it downed or drove off its assailants and escaped. Such actions — and the type’s general refusal to be an easy victim — gave rise to the porcupine nickname. As with many wartime stories the finer details deserve some caution, but the underlying truth is sound: the Sunderland was very well defended, and it bit back hard.

The Sunderland’s central mission was hunting submarines. Early in the war its ability to do so was limited, but as technology matured it became a formidable U-boat killer. Air-to-surface-vessel (ASV) radar let it detect surfaced submarines by day, at night and in poor visibility; depth charges with shallow settings, dropped in a straddle across a diving boat, gave it a genuine killing weapon; and later aircraft added forward-firing guns to suppress the flak that surfaced U-boats put up to fight back.

Across the war Sunderlands were credited, alone or jointly with ships and other aircraft, with sinking a significant number of U-boats, and with damaging and harassing many more. Just as important as the confirmed kills was the deterrent effect: a Sunderland overhead forced submarines to dive, blinding them and slowing them, and kept them away from the convoys. In the long attritional Battle of the Atlantic, that constant pressure was decisive.

The Sunderland was one of the signature aircraft of RAF Coastal Command, the force charged with the maritime war: anti-submarine patrol, convoy escort, reconnaissance and anti-shipping strikes. The Battle of the Atlantic — the struggle to keep the sea lanes to Britain open against the U-boats — was the longest campaign of the war and, in Churchill’s judgement, the one thing that truly frightened him.

Long-range aircraft were the key to winning it, and the Sunderland’s enormous endurance let it patrol far out into the ocean and escort convoys through the dangerous mid-Atlantic. Working alongside the American-built Catalina and, later, very-long-range Liberators, the Sunderland helped close the air gaps where U-boats had hunted freely, contributing directly to the turning of the Atlantic battle in the Allies’ favour in 1943.

Endurance was the Sunderland’s defining quality. Patrols of thirteen hours or more were routine, and the aircraft could range far out over the ocean and loiter for hours in the patrol area — exactly what anti-submarine work demanded. As a flying boat it did not need a runway; it operated from sheltered water, which suited a global maritime war fought from bases scattered around coasts and islands.

The flying-boat approach had costs, too: performance was modest, the aircraft was large and relatively slow, and operating from water brought its own hazards of weather, swell and mooring. But for the specific job of very-long-range ocean patrol in the 1940s, before land-based aircraft had the range and before mid-ocean airfields existed, the big flying boat was an outstanding solution — and the Sunderland was among the very best of the breed.

The Sunderland improved steadily through its marks. The early Mk I and Mk II were powered by Bristol Pegasus radial engines and progressively gained better turrets and, crucially, radar. The Mk III, the major wartime production version, introduced a revised planing hull that improved the aircraft’s behaviour on the water.

The most significant change came with the Mk V, which replaced the increasingly overtaxed Pegasus engines with American Pratt & Whitney R-1830 Twin Wasp radials. The Twin Wasps gave more power, better high-altitude performance and greater reliability, and cured the tendency of the older engines to be worked beyond their limits by the ever-heavier late-war aircraft. The Mk V became the definitive Sunderland and the version that soldiered on into the post-war years.

Because it could land on the open sea, the Sunderland was ideally suited to air-sea rescue, and it saved many lives in that role. It could alight beside downed aircrew or shipwrecked sailors in the water, take them aboard through its hull hatches, and fly them to safety — something no landplane could do.

This humane, dangerous work — landing a large aircraft on an open ocean swell was never routine — ran alongside the Sunderland’s combat missions throughout the war and after it. For a downed airman drifting in a dinghy in a cold sea, the sight of a Sunderland settling onto the water nearby was, quite literally, salvation. It is one of the aircraft’s most sympathetic and least-celebrated contributions.

One of the Sunderland’s more remarkable post-war chapters was the Berlin Airlift of 1948–49. When the Soviet Union blockaded West Berlin, the Allies supplied the city entirely by air, and RAF Sunderlands took part — flying from the Elbe near Hamburg and alighting on the Havel lake inside Berlin to unload their cargo.

The Sunderlands had one particular advantage: their marine hulls were built to resist salt water and corrosion, which made them ideal for carrying the corrosive cargo of salt that ordinary transport aircraft struggled with. It was an inspired, improbable use of a maritime patrol aircraft — a flying boat helping to keep a landlocked city alive by landing on its lakes — and a vivid illustration of the type’s versatility.

The Sunderland was built in a series of marks — Mk I, II, III and V being the main service versions, with detail improvements in turrets, radar, hull form and engines along the way (the enlarged Mk IV was developed into a separate type, the Seaford). The Mk III was the major wartime version and the Mk V, with Twin Wasp engines, the definitive late and post-war one.

The type’s combat career did not end in 1945. During the Korean War, RAF Sunderlands of the Far East Flying Boat Wing flew maritime patrol and blockade missions from Iwakuni in Japan, operating over Korean waters. It was a striking demonstration of the design’s longevity that a flying boat conceived in the mid-1930s was still flying front-line patrols in a jet-age war in the early 1950s.

As with other British wartime aircraft, there is no reliable, transparent public figure for the Sunderland’s unit cost, cost per flight hour or total programme cost. It was procured by a wartime state economy that did not publish such accounts in a consistent, comparable form, and surviving records are incomplete. Any single figure quoted for it should be treated with caution.

In broad terms, a large four-engine flying boat was an expensive and manpower-intensive aircraft to build, operate and maintain — it needed marine facilities, moorings and beaching gear as well as ordinary airfield support, and it carried a big crew. That cost was justified by a capability nothing cheaper could match: very-long-range ocean patrol. We list the cost fields as “not reliably recorded” rather than invent numbers.

The Sunderland’s hull lived on in civil aviation. After the war, Sunderlands were converted, and further developed, into the Short Sandringham and Short Solent airliners, which carried passengers in the spacious, comfortable style of the great flying-boat era for airlines including BOAC. These graceful machines were among the last of the big passenger flying boats, and a few survive in museums as reminders of that vanished way of travel.

Militarily, the Sunderland served well beyond the RAF. The Royal Australian, Canadian, New Zealand and South African air forces all operated it, and after the war the French Aeronavale and the Royal Norwegian Air Force flew Sunderlands on maritime patrol. New Zealand kept the type in service longest of all, flying Sunderlands into the 1960s — a measure of how useful the big flying boat remained even into the jet age.

Because it was built in reasonable numbers and served long into the post-war years, the Sunderland has left several survivors, more than many wartime types. Complete examples are preserved at major museums including the Royal Air Force Museum and the Imperial War Museum in the United Kingdom, and others survive in New Zealand and elsewhere, along with civil Sandringham/Solent derivatives in collections around the world.

No Sunderland flies today — keeping a large four-engine flying boat airworthy is an enormous undertaking — but the surviving static examples let visitors walk through the two-deck hull and see the galley, bunks and gun positions for themselves. To stand inside one is the best way to grasp what the crews meant when they called it a ship rather than a plane.