How the 1930s Royal Navy settled on a strategy to deal with a rapid pace of change and a challenging set of requirements.

It is often said that the battleship died because it was vulnerable: this cannot be correct since the new capital ship, the carrier, was far more vulnerable. The battleship died because it had very little capability for damaging the enemy.
— Brown, D. K: Nelson to Vanguard: Warship Design and Development

Striker or survivor: A matter of mission

AN aircraft carrier is a remarkably complex weapons system.

Not only must it address conventional naval requirements (protection, armament, endurance and speed), it must also accommodate a whole new set of problems (aircraft stowage, operation and supply).

Its aircraft are its primary armament. They are also its eyes.

Exactly how it addressed, met and used all of the above was the subject of much debate and theorising among all the worlds’ major navies during the inter-war years.

Britain – with its unique requirement of having to operate in the North Atlantic, Mediterranean, Indian and Pacific Oceans – eventually adopted a somewhat individual approach.

Initially the idea was similar to that followed by the United States and Japan. After all, they were the only other major naval powers operating aircraft carriers. Such a fight, naturally, would likely happen in the broad expanses of the Pacific where endurance and large air-groups were necessary. It was for just such a scenario that HMS Ark Royal was designed.

But, closer to home, the threat of the land-based bomber was paramount. The Royal Navy expected to have to face large numbers of these from Germany and Italy. It also expected to have to operate in narrow waters dominated by enemy aircraft.

The Home Fleet’s operations in the North Sea extended to what the Royal Navy saw as the potential need to escort and support a British Army Expeditionary Force through a hostile Baltic Sea – with the straights between Denmark and Sweden of particular concern. North Sea operations also included the imperative of homeland defence. For Great Britain, this inevitably meant fighting in the narrows of the English Channel.

The initial expectation, however, was for fleet carriers to not to have to operate close to land.

German propaganda claiming the sinking of HMS Ark Royal.

German propaganda claiming the sinking of HMS Ark Royal.

CLICK FOR LARGER VIEW: Ark Royal, with her two hangars, was designed with the Pacific theatre in mind.

In 1935/36 when the political situation was causing some anxiety, careful thought was given to the part that an aircraft carrier would play in a future war. The aircraft, it was realised, would be the ‘eyes’ of the Fleet as well as being both attackers and defenders in an engagement, and consideration was therefore given to the protection of the aircraft themselves.
— The Design and Construction of British Warships 1939-1945 - Major Surface Ships

Turning turtle

In 1935 Britain felt war was imminent with Italy. The Abyssinian crisis suddenly shifted its strategic focus away from war in the Pacific against Japan, to fighting in the narrow confines of the Mediterranean against Italy.

War would eventually break out in both theatres. But it was the Mediterranean scenario which unfolded first.

The foot of Italy and Sicily acted as a natural barrier between Gibraltar in the west, and Greece, Crete, Egypt and Palestine in the east. The invaluable base of Malta right at the heart of the choke-point was both an asset and a liability. Defending it meant incredibly risky convoys running the gauntlet of submarines, main-fleet warships and land-based aircraft. But it also offered an unsinkable base of operations right in the centre of Axis supply lines between Europe and North Africa.

Finally, there were Britain’s interests in the Pacific. At first pass one may think the Royal Navy’s requirements would be no different to that of the United States. Then one looks at the position of Singapore (amid the Indonesian and Malay archipelagos) and the proximity of Hong Kong to the Chinese mainland. 

With the confined nature of many of these waterways, the proximity to hostile naval bases and the expectation of operating continuously under the umbrella of large numbers of land-based aircraft, the Royal Navy saw carriers as particularly challenged. Enemy cruisers, destroyers and torpedo boats could sortie at short notice and engage a carrier group within gun range. Submarines could picket narrow channels. Battleship and battlecruiser forces could blockade shipping lanes and ports.

But it was the many advantages which land-based aircraft had over carriers which clinched the deal in the mind of the Admiralty. The fighters were generally larger and faster. Bombers could range anywhere from single-engine attack craft through to four-engine high-altitude machines. The expectation was to contend with large numbers of superior enemy aircraft. 

Given these considerations, the armoured carrier was quickly judged the most viable prospect.


(Admiral Sir) Reggie (Henderson) hated paperwork and just could not wait for Staff Requirements to be prepared ... and it was his decision to go ahead without them, which led to the great saving in time in placing orders for the ship. Sir Arthur Johns (then Director of Naval Construction) was sick and absent from the Admiralty (he never returned), his deputy Mr. Fred Bryant was fully occupied in running the department, which was exceedingly busy, so Reggie just sent for me and told me he wanted a fully armoured carrier with a flight deck proof against 500 pound bombs and armour on the sides of the hangar equal to that used for contemporary cruisers. Most of the rest he left to me.

For about two months he sent for me each Friday afternoon and after I had told him how I was getting on, he would stride up and down that great room of his at the Admiralty and talk and talk, and if he stopped for breath I would put in a word and off he would go again. Nobody else was present at these talks.

Head of the Aircraft Carrier design section at the Admiralty during the armoured carrier programl, W.A.D. Forbes.

Full title reads: "North Sea Special - The Navy In Action". GV Bow of battleship rising and then falling amidst clouds of spray as the ship ploughs through the rough sea. Good CUs and MSs of the crew of battleship, all dressed in heavy clothing against the cold, manning guns and lookout positions around the ship in anticipation of an air attack.

The British desire to protect aircraft from weather as well as enemy attack led both to the closed hangar and, later, to the armoured hangar
— D.K. Brown: Nelson to Vanguard: Warship Design and Development 1923–1945

Alternate reality

The Admiralty of the 1930s believed carrier air wings would be overwhelmed by numbers, quality and exhaustion when operating under a hostile land-based umbrella. 

To this end the idea was for a carrier’s fighters to be “struck below” in a protected space while the ship’s heavy and light anti-aircraft armament took up the defence along with its escort. This was particularly relevant in a world without radar for early warning or direction of air-patrol interceptions.

When combined with the Royal Navy’s low expectations as to the effectiveness of carrier-based aircraft, one can understand why they settled on armoured carriers.

Skewed purpose ... The Blackburn Skua was a dive bomber given a secondary role as escort fighter in an era where there was insufficient early warning for effective fleet-defence interception.

Skewed purpose ... The Blackburn Skua was a dive bomber given a secondary role as escort fighter in an era where there was insufficient early warning for effective fleet-defence interception.

The Royal Navy Air Office of the 1930s insisted that naval aircraft required a pilot, observer and gunner. The challenges of navigating to a target, spotting a target - accurately determining its position - and returning to a ship over the featureless expanses of ocean (without radar) were simply too great for a single pilot to achieve, they believed.

Another belief was imposed by the RAF: that carrier aircraft would not deploy bombs heavier than 500lb. This short-sightedness was to have unfortunate consequences in the extent of armour protection provided for British cruisers, battleships and carriers throughout the war.

But reality quickly forced compromises. Radar changed everything. The early warning needed to direct carrier-based fighters to intercept incoming attackers was now suddenly available.

Several alternative designs had to be worked out before I could get a fully armoured carrier of 23,000 tons and one of the main secrets was that the 3 inch armour plate which formed the flight deck was used both for protection and longitudinal strength. No backing was used under the armour. The 3 inch armour, worked structurally, with riveted and rabbeted laps and butts was worked on the flight deck and 4½ inch on the hangar sides.
Immediately Reggie was satisfied, an official ’sketch design’ was submitted to the Board by Mr. Bryant and Reggie bulldozed it through and got Board approval in a month, an unprecedented speed. Shortly after this approval of the ’sketch design’ was given Mr., afterwards Sir, Stanley Goodall was appointed Director of Naval Construction and so the ‘Building Drawings and Specification’ were prepared under his supervision and he signed them in due course before they were submitted for Board stamp.
Sir Stanley had not had much previous experience of carriers. It so happened that I was uniquely equipped to undertake the job. I was familiar with all existing carriers and had witnessed many hundreds of landings of all types of aircraft, and moreover I had the recent experience of being the Constructor in charge of the Ark Royal design. There were few people who had the necessary experience of carriers to do the job (your father was one of the few).’

In the above letter to Alan Payne, Mr. Forbes described the unorthodox design of the armoured carriers.

A high performance single-seat fighter suddenly became a naval necessity. Early attempts at adapting the Hurricane and Spitfire in 1941 proved successful - though imperfect. But these aircraft could be pitched against land-based opponents on something approaching an equal footing.

This left the concept of the armoured carrier hanging. Was enhanced protection at the price of smaller air groups still relevant?

Victorious ... The Abyssinian crisis of the mid 1930s shifted the Royal Navy's attention away from the Pacific to the Mediterranean.

Victorious ... The Abyssinian crisis of the mid 1930s shifted the Royal Navy's attention away from the Pacific to the Mediterranean.

I would suggest that both the RN and USN were right for the wars they planned to fight , the RN in narrow seas, facing shore-based aircraft while the USN expected to engage the Japanese fleet in the open Pacific.
— D.K. Brown: Nelson to Vanguard: Warship Design and Development 1923–1945


By the mid 1930s the Royal Navy had set its course for future carrier development. Fleet exercises had demonstrated that the air threat was serious and that some would “always get through”.

This implied that carriers would be subject to damage.

And carriers were believed to be particularly vulnerable. All it would take was one bomb hit on the deck to render at least half of it inoperable.

Controller Rear Admiral Reginald Henderson - also the Royal Navy's most experienced carrier commander - faced two divergent means of countering this threat: One was to cram as many defensive fighters into the ship as possible, the other was to maximise the ship’s own passive and active resistance to damage.

He settled on the second option.

A 1940s animated representation of the ILLUSTRIOUS flight deck from an FAA instructional film.

A 1940s animated representation of the ILLUSTRIOUS flight deck from an FAA instructional film.

Providing a carrier more guns and more armour would give it the best overall chance of survival, he felt. After all, the flimsy and vulnerable aircraft of the 1920s and 30s were not exactly impressive. And naval aircraft were even less so.

US and British naval war games demonstrated the carrier fleet that usually won was the first to get off an air strike - even if it was a much smaller force.

There were several divergent solutions to this: Build more, smaller, hulls to reduce the impact of such a first-wave strike (one proposed US solution) or build ships more capable of surviving such an attack.

It was a consideration also key to the carrier's role in the battlefleet. The US judged that it was best to disperse its carriers individually, with small escorts, to reduce the chance of their discovery and to minimise losses. The RN resolved to keep the carrier at the heart of the battle group, and initiated a program of rebuilding battleships and battlecruisers (and introducing new anti-aircraft cruisers) to provide an anti-aircraft screen.

Controller Henderson understood the circumstances under which British aircraft carriers would be required to operate in Europe and the Mediterranean. This meant within the range of land-based bombers and short sortie distances for forces of cruisers and destroyers.

He took these threats very seriously.

He also had valuable insight into the operation and requirements of fleet carriers: As a Rear-Admiral in 1933, Henderson had been in command of all RN carriers. During this time he had experimented with operating Furious, Courageous and Glorious as a single strike force. He became keenly aware of carrier capabilities - and vulnerabilities - during the Abyssinian Crisis of 1935.

Japan and American operated under different circumstances. Both were considerable distances from any real or perceived threat, and their ships would therefore be mostly operating in the vast expanse of open oceans.

The threat of fast cruiser raids was real, they thought. But land-based bombers were only a remote hazard. As a result, the US Navy and Imperial Japanese Navy armed their early carriers with 8in guns but gave them only light anti-aircraft outfits.

The Royal Navy regarded the big guns as redundant aboard carriers: After all, what was the escort for? Instead, Britain focused on including as many dual-purpose guns as possible in their designs. While providing a strong anti-aircraft barrage, these 4.5in weapons would also be of some use if required to repel a small-ship surface attack.

Admiral Henderson’s biggest concern was having his limited number of carriers unable to carry out their primary function: launch, land and service aircraft. Gunfire and bombs could quickly render the hangar and flight deck inoperable. 

His solution: a protected hangar, with armour embracing the space on the top and sides.
His challenge: to overcome the weight, stability and hangar space problems entailed by building such ships within the restrictions of the naval treaties.

There was another problem: The treaties allowed Britain five 27,000 ton carriers.

The Royal Navy wanted six.

The solution: Smaller 23,000 ton ships.

HMS Illustrious, Formidable and Victorious were the result of these requirements and restrictions.
They emerged in the opening years of the 1940s as effective ships, but concerns had been growing about the size of their air group from the outset.

Their official capacity was only 33 aircraft – based on British standards of how many aircraft could be neatly stowed away from the wild North Atlantic weather in their enclosed hangars.

But Britain's understanding of the importance of naval air power is evident in the fact that, in 1939, the Royal Navy was building more carriers than any other nation.


The driving force behind the Royal Navy's radical shift towards heavily armoured aircraft carriers was Admiral Sir Reginald Henderson GCB.

Understanding his experiences goes a long way to explaining the doctrine that produced HMS Illustrious and her sisters.

Henderson early career had seen him become a gunnery specialist - always a high-profile title to have at the time. He served on the Admiralty's Naval Staff during World War I where he worked to improve anti-submarine tactics and convoy defence.

Generally regarded as an innovative and creative officer, he was given command of the aircraft carrier HMS Furious after the war.

By 1933, he had been made Rear Admiral Aircraft Carriers.

In this role he took his force of ships - HMS Furious, Corageous, Glorious, Hermes and Eagle - and developed  the RN's own doctrine for multi-carrier strike forces. This was something of an achievement given the RAF's control over his aviation.

In particular, Henderson placed heavy emphasis on night strike tactics. He saw this as a viable solution to the one problem that kept presenting itself to Japanese, United States and British carrier commanders: the fleet that got in the first successful strike always won.

Extending the opportunity to launch a torpedo strike to 24-hour-a-day would give RN forces a decided advantage, he felt. 

Where Henderson failed, however, was convincing the RAF that dive-bombing was a powerful technique against surface ships. It refused to accept his argument that it held significant advantages in accuracy over level bombing.

By 1935 Henderson was promoted to the prestigious - but stressful - role of Controller. This title was given to the Admiralty Board Member responsible for the capabilities and designs of new warships.

It gave him the opportunity to put into effect the lessons he had learned operating and coordinating his carriers. 

Henderson would work closely with naval architect W.A.D Forbes, who was responsible for carrier design, to both fast-track and bulldoze-through his ideas for an armoured carrier.

It was not without controversy. Many in the Naval Staff - including Dennis Boyd who would become HMS Illustrious' first captain - would resent their lack of involvement in this process.

But Henderson insisted his carriers had to be able to stand up to sustained attack from land-based bombers.  He also knew the price for all this protection would be heavy; including a reduced air group and restricted maintenance abilities. 

Henderson had closely watched the RN's carrier ops unfold in the Mediterranean during the Abyssinian Crisis, and saw the high attrition intensive deck operations produced. So he ordered the design and construction of a fleet maintenance carrier - HMS Unicorn - and the hangar revisions that would produce HMS Indomitable.

Admiral Henderson resigned due to ill-health related to over-work in March 1939. He died just two months later.

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