Royal Navy Implacable Class Aircraft Carriers: A Comprehensive Guide

The Implacable class aircraft carriers represented the final evolution of the Royal Navy’s pre-Second World War fleet carrier design philosophy. Conceived as an improved version of the Illustrious class, they combined strong armoured protection with greater aircraft capacity, answering the criticism that the earlier class carried too few aircraft.

Only two ships were completed, HMS Implacable and HMS Indefatigable, both of which served with distinction in the closing stages of the war and went on to have long post-war careers.

Origins and Design Development

By the late 1930s, the Royal Navy had embraced the concept of armoured flight decks, prioritising survivability over the size of the air group. However, combat experience during the early years of the war revealed that the Illustrious class could not carry enough aircraft to sustain prolonged operations.

The Admiralty responded with the Implacable class, which sought to combine the protective features of the Illustrious class with a larger hangar capacity.

The result was a carrier design displacing around 23,500 tons standard and over 32,000 tons fully laden, with a length of 766 feet. The ships retained armoured flight decks and hangars but were designed with two hangar levels, increasing aircraft capacity to approximately 81 aircraft when fully loaded.

This nearly doubled the carrying capacity of their predecessors.

The Two Feet That Decided Everything

It also cost them, and the price is the most important fact about the class. Both ships were laid down in 1939 and spent five and a half years building, because a big fleet carrier that would not be ready for years kept going to the back of the queue behind escorts, merchant repairs and landing craft. While they sat there the design was reworked: an extra turbine and shaft for more speed, thicker hangar side armour, and a lower hangar stretched forty-six feet further forward than Indomitable's.

All of that had to be paid for in weight, and it was paid for by taking two feet out of the height of the lower hangar. Both hangars ended up with fourteen feet of clearance. It was a sum done on paper in 1940 to balance a displacement figure, and it defined the rest of both ships' lives.

Fourteen feet does not sound like a constraint until you try to put an aeroplane under it. The Vought Corsair, the best carrier fighter the Allies had by 1944, would not go in at all even with its wings folded. Hellcats were not available in the numbers needed. So where the other British carriers in the Pacific flew American aircraft, these two went to war with Seafires: beautiful aeroplanes, marvellous to fly, and quite unsuited to carrier work, with narrow-tracked undercarriages that broke on hard landings, poor forward visibility on the approach and a combat radius so short that a Seafire on patrol could not go far from the ship.

So the paper figure of 81 aircraft is real and the capability behind it was not what it looks like. The Illustrious class carried fewer aircraft and could operate better ones.

Their propulsion systems gave speeds of around 32 knots, making them among the fastest British carriers of their time and allowing them to operate effectively alongside the United States Navy’s fast carrier task forces in the Pacific.

Ships of the Class

Only two ships of the planned class were completed due to wartime constraints:

HMS Implacable (R86)

HMS Indefatigable (R10)

Several other ships were planned but cancelled as priorities shifted during the war.

HMS Implacable (R86)

HMS Implacable (R86) was built by Fairfield at Govan, laid down on 21 February 1939, launched in December 1942 and commissioned on 28 August 1944, the lead ship of the class and five and a half years in the building.

Her first operation came barely two months later. She sailed from Scapa Flow on 16 October 1944 to attack Tirpitz, found her two days afterwards anchored off Hakoya Island near Tromso, and had to break off without pressing home an attack, having no fighter escort of her own and Luftwaffe airfields close at hand. It was one of the last naval attempts on the ship; three and a half weeks later the RAF finished her with two Tallboys.

She made up for it that November with Operation Athletic, a sweep along the Norwegian coast in which her aircraft claimed six ships and a U-boat for the loss of a single Barracuda. That was dangerous work: the German iron ore came down from Sweden in small coasters running inside the leads, and attacking them meant flying at low level in narrow fjords ringed by mountains and flak, with nowhere to go if you were hit.

She joined the British Pacific Fleet in 1945, struck the bypassed Japanese base at Truk on 14 and 15 June in Operation Inmate, flying 113 sorties over two days for the loss of one Seafire, and then went on to strike the Japanese home islands as part of Task Force 37, the British component of Admiral Halsey's Third Fleet. Her aircraft flew over a thousand sorties in the Pacific. Afterwards she carried liberated prisoners of war home.

HMS Indefatigable (R10)

HMS Indefatigable was commissioned earlier, in 1944, and saw immediate action. Her first operational sortie was Operation Mascot against Tirpitz on 17 July 1944, and she went back for Operation Goodwood that August. Both achieved nothing at all, because the Germans had the smoke generators going long before the Barracudas arrived. She then joined the British Pacific Fleet alongside her sister ship.

In 1945, Indefatigable’s aircraft launched repeated strikes against Japanese positions, including raids on airfields and shipping. She was present during the final months of the war and contributed to operations that weakened Japanese resistance.

Before any of that came Operation Meridian in January 1945, the strikes on the refineries at Palembang alongside HMS Illustrious (87), HMS Indomitable and HMS Victorious, which cut Sumatran output to about a third at a point when Japan was desperately short of aviation spirit. It cost forty-one aircraft and thirty aircrew killed, with nine more captured and murdered after the surrender.

Easter Sunday, and Thirty-Seven Minutes

One morning off Okinawa makes the case for an armoured flight deck better than any specification can. At 07:28 on Easter Sunday, 1 April 1945, a Japanese Zeke carrying a 550lb bomb came at Indefatigable through her own Seafires, was hit by cannon fire on the way in, appeared to break apart mid-dive and struck the ship anyway, at the point where the flight deck met the island.

It depressed the armoured deck about three inches over a fifteen-foot area, destroyed the radio office, the flight deck sick bay and the pilots' briefing room, damaged three parked aircraft and started fires that went into the island. Fourteen men were killed, eight outright and six later of their wounds, among them the Lieutenant Commander (Flying), the Air Engineering Officer and the Flight Deck Medical Officer. Thirty-two more were wounded.

And she was landing aircraft again at 08:16, thirty-seven minutes after being hit, on a single working crash barrier. Ruptured high-pressure steam pipes in the island had helped smother the fire within four minutes. That is what an armoured flight deck was for, and it is the reason the British insistence on one stopped looking like an eccentricity in 1945 and started looking like foresight.

Post-war, Indefatigable continued in service as a training carrier, helping to prepare new generations of naval aviators. She paid off on 3 September 1954 into reserve at Rosyth, was sold the following year, and was broken up between November 1956 and April 1959.

Technical Features

The Implacable class incorporated several technical improvements over earlier carriers:

Displacement: Around 23,500 tons standard, 32,110 tons full load.

Length: 766 feet.

Speed: Up to 32.5 knots from steam turbines driving four shafts

Flight Deck: Armoured for protection against bombs and kamikaze strikes.

Aircraft Capacity: Up to 81 aircraft, almost double the Illustrious class.

Armament: Included 4.5-inch dual-purpose guns and numerous anti-aircraft weapons.

The addition of a double hangar was the most significant design change, addressing the key shortcoming of previous carriers.

Operational Service and Legacy

Although they arrived late in the Second World War, the Implacable class played a valuable role in the Pacific. Their ability to operate larger air groups made them more compatible with the American Essex class carriers they often served alongside.

Their armoured decks proved effective against Japanese air attacks, and their operational endurance allowed them to sustain operations far from home waters. After the war, both ships contributed to training and peacetime duties, but post-war defence cuts and rapid advances in naval aviation limited their long-term usefulness.

Ten Years, and Never Once Hit

The reason both went so quickly takes us back to the two feet. By the early 1950s carrier aviation meant jets. Jets were larger and heavier than anything either ship had been designed around, and a hangar with fourteen feet of headroom could not take them. Neither could the lifts, and neither could the decks.

They could have been rebuilt. Doing it properly would have cost close to the price of a new ship, which is why the money went into the Audacious class instead. So HMS Implacable (R86), a carrier that had hunted Tirpitz off Norway, swept the Norwegian leads, struck a bypassed Japanese fortress at Truk, flown against Tokyo alongside the United States Third Fleet and then carried starved prisoners home, paid off on 1 September 1954 after ten years in commission and went to the breakers at Inverkeithing, having never once been hit by anything.

It is the clearest illustration in the fleet of something true of most warships: how long a ship lasts is usually decided years before she floats, by people doing sums.

The class demonstrated that Britain could build large, heavily armoured carriers capable of matching the operational tempo of other major navies. While their service lives were relatively short compared to some ships, they bridged the gap between the wartime fleet carriers and the post-war generation of modernised carriers.

A Fine Ship Built Two Feet Too Short

The Implacable class aircraft carriers were the Royal Navy’s answer to the limitations of earlier designs. They successfully combined armoured protection with significantly larger air groups, ensuring Britain could field competitive carriers during the climactic final campaigns of the Second World War.

Although their post-war service was relatively brief, their influence on carrier design and their contributions in the Pacific left an enduring mark on naval history.