Armoured Flight Deck - Defences

Defences

The British approach of armoured flight decks was an effective form of passive defence from bombs and kamikaze attacks that actually struck their carriers, but the American carriers primarily relied on fighters to prevent the carriers from being hit in the first place. RN carriers such as Ark Royal or Illustrious had far heavier AA outfits than their USN counterparts, up to the introduction of the USN Essex class carriers. Ark Royal, in 1940, carried 16 x 4.5-inch guns, 32 x 40mm "Pom-pom" and 32 x 0.5 inch against 8 x 5", 16 x 28mm and 24 x .5" for Enterprise, in 1940. "In wartime, however, the US Navy found the armoured carriers fascinating. After having examined HMS Formidable in 1940, the US naval attaché commented that, were he crossing the Pacific, he would prefer her to a Yorktown, the closest US equivalent, on the basis that she might carry fewer aircraft, but she would be much more likely to get there". Late in the war when the USN operated many carriers together and had improved radar, their fighter and AA defence was reasonably effective, yet both conventional and kamikaze attacks were still able to penetrate USN defences. Bunker Hill and Franklin nearly succumbed in 1945. The larger air groups (80–110 planes, vs. 52–81 for late war British ships) allowed for a more effective combat air patrol (CAP) without reducing strike capability, improving the protection of the whole battle group and lessening the workload of the carrier escorts. Carrier fighters were able to shoot down far more kamikaze aircraft than any amount of deck armour would have protected against showing the value of absolute numbers, but in the early war period IJN aircraft had little difficulty in penetrating USN CAPs; near the end of the war, veteran American fighter pilots in superior F6F Hellcat and F4U Corsair fighters were able to defeat the young, inexperienced and ill-trained kamikaze pilots with ease and run up huge kill scores but attackers were still able to get through. (In addition to larger aircraft complements, the US Navy had larger fleets and more resources, so they could establish destroyer pickets and develop dedicated AAW ships such as the Atlanta-class antiaircraft cruisers which would have also drawn attention away from the carriers.) On the surface, the record seems balanced.

British naval historian D.K. Brown put the practical difference between American and British design philosophies in no uncertain terms: "More fighters would have been better protection than armour." but that British designs were good for the circumstances in which they were meant to be used. Yet, even the Ark Royal, Britain's newest carrier prior to WW2, never operated close to her theoretical aircraft capacity. Prior to the development of effective Radar and high speed monoplane fighters, a successful fighter defence was extremely unlikely for any navy thus calling into doubt D.K. Brown's conclusions. The benefits of flight deck armour were intended to counter these issues. Fewer aircraft meant a lower priority to attack than the more heavily-armed American carriers and the RN's operational doctrine dictated smaller airgroups, and the armoured hangar carriers had smaller Avgas and ammunition supplies to match. However, RN carriers carried far more aircraft later in the war, making use of the deck park when they adopted USN style operational doctrine. The 2nd generation RN armoured carriers, Indomitable and the Implacable class which had an additional half length lower hangar, were considerably less outmatched by their USN counterparts in the numbers of aircraft operated. The RN operating in harsher weather protected their aircraft from the elements and did not use a permanent deck park in the earlier part of the war. US carriers and their fighters shot down more than 1,900 suicide aircraft during Operation Kikusui (the last and largest Kamikaze attack in the Okinawa campaign), versus a mere 75 for the British, yet both forces suffered the same number of serious hits (four), on their carriers. However the kamikazes made 173 strikes against other USN targets and the 4 USN carriers suffered a massive death toll, in contrast to the relatively light casualties on the RN carriers.

The kamikaze threat overall was serious, but allied defences neutralised it, and many kamikaze strikes missed the deck armour entirely, or bounced off the decks of both British or American carriers. In some cases, kamikazes either struck glancing blows that did only superficial damage that was fixed within minutes or hours, or missed entirely, due to the poor training and poorer flight experience of their pilots. The majority of kamikazes that did inflict harm caused no more damage than they would have against smaller ships. After a successful kamikaze hit, the British were able to clear the flight deck and resume flight operations in just hours, while their American counterparts often could do the same, but not always; in some cases repairs took a few days or even months. The USN liaison officer on HMS Indefatigable commented: "When a kamikaze hits a U.S. carrier it means 6 months of repair at Pearl . When a kamikaze hits a Limey carrier it’s just a case of "Sweepers, man your brooms."”

American carriers of the Essex class suffered very high casualties from serious kamikaze hits, though they did survive. USS Franklin was struck by two 250 kg(550 lbs) bombs, one semi-armour piercing (SAP) and one general purpose (GP), both of which penetrated into her hangar and set off ammunition, killing 724 personnel. USS Bunker Hill was severely damaged by pair of kamikaze hits which killed 346 men. Each of these USN carriers suffered more casualties than all the British RN armoured carriers combined, illustrating the life saving features of RN carrier design. Illustrious, which had the highest toll, suffered 126 fatal casualties and 84 wounded when hit by six 1100 lb bombs on 10 January 1941. The USN studied the superior defensive qualities of Royal Navy armoured carriers and this analysis is partly revealed in the damage report following the attack on Franklin on 13 March 1945:

As a result of study of damage sustained by various British carriers prior to our entry into the war, two important departures from traditional U.S. Navy carrier design were incorporated in the CVB Class, then still under development. HMS ILLUSTRIOUS in an action off Malta on 1 January 1941 was hit by several bombs, three of which detonated in the hangar space. Large fires swept fore and aft among parked planes thereby demonstrating the desirability of attempting to confine the limits of such explosions and fires by structural sectionalization of the hangar space. On the CVB Class the hangar was therefore divided into five compartments separated by 40 and 50-pound STS division bulkheads extending from the hangar deck to the flight deck, each fitted with a large door suitable for handling aircraft. It is hoped that this sectionalization, in conjunction with sprinkler and fog foam systems, will effectively prevent fires from spreading throughout the hangar spaces, as occurred on FRANKLIN on 30 October and 19 March. The damage experiences of several British carriers, which unlike our own were fitted with armoured flight decks, demonstrated the effectiveness of such armour in shielding hangar spaces from GP bombs and vital spaces below the hangar deck from SAP bombs. Accordingly, the CVB Class was designed with an armoured flight deck consisting of 3-1/2-inch STS from frames 46 to 175 with a hangar deck consisting of two courses of 40-pound STS between frames 36 and 192. Although none of the CVB Class carriers were completed in time to take part in war operations, the effectiveness of armoured flight decks against Kamikaze attacks was demonstrated by various carriers attached to the British Pacific Fleet. Reference (k) reports two such interesting cases. The VICTORIOUS was struck by three Kamikaze aircraft, two of which ricocheted off the armoured flight deck and over the side, causing no important damage. The third carried a bomb which detonated at frame 30 starboard at the butt of the 3-inch flight deck armour with 1-1/2-inch "D" quality (equivalent to HTS) steel. It does not appear that the Kamikaze actually struck the ship. The bomb detonation, however, depressed the 3-inch deck slightly but did not tear it open. On the other hand, the 1-1/2-inch "D" quality deck plating was ripped open over a total area of about 25 square feet. Two days were required for temporary repairs, at the conclusion of which the ship was fully operational. HMS FORMIDABLE was hit by two bombs, the first of which struck and detonated on the flight deck 9 feet to port of the center-line at frame 79, directly over a deep bent and at a juncture of three armoured plates. The armoured deck was depressed over an area 24 feet long and 20 feet wide. Maximum depression was 15 inches. Adjacent bents spaced 12 feet forward and aft of the point of impact were slightly depressed. A hole 2 square feet in area was blown in the 3-inch deck. Three fragments penetrated downward through the ship into the center boiler room. The damage in this boiler room, which was not described, temporarily reduced speed to 18 knots. The second bomb struck and detonated on the centreline of the flight deck at frame 94. The 3-inch deck and deep bent directly below the point of impact were depressed about 4-1/2 inches and one rivet was knocked out. However, the ship was fully operational within about 5 hours, including flight operations. —

The only Allied carrier lost to a deck hit was the American Independence-class light carrier, USS Princeton (CVL-23). Indeed, many light and escort carriers were unarmoured, with no protection on the hangar or flight deck, and thus they fared poorly against deck hits.