Armoured flight deck
The remainder of the IJN carrier force during World War II had unarmoured flight decks just like the Yorktown and Essex classes of the USN.
The USN open hangar design allowed large numbers of aircraft to be warmed up while inside, theoretically reducing the time required to range and launch a strike, but storage of fuelled and armed aircraft in an unarmoured hangar was extremely dangerous: ...Captain John S. McCain of the Ranger...actually preferred a relatively small carrier, as long as it could be protected against bombing.
[9] American carriers after the Lexington-class, and the earlier Japanese carriers, had their armour placed at the hangar deck, essentially treating the hangar spaces and flight deck as superstructure – making these areas very vulnerable to the blast from GP bombs and other explosions, which in turn caused massive casualties in comparison to RN designs.
Such a design allowed for larger, open-sided hangar bays (improving ventilation but making the ship very vulnerable to chemical weapon attack) and the installation of deck-edge elevators.
Prior to WWII the RN and USN both recognised that the dive bomber could disable the flight decks of enemy aircraft carriers: ...From about 1933 on, the Admiralty showed increasing interest in dive-bombing, as the best means of accurate delivery against small and highly manoeuvrable ships.
Dive-bombing was also particularly attractive as a means of neutralizing enemy aircraft carriers, which some in the Fleet Air Arm considered their primary targets.
British observers seem to have been impressed by US demonstrations...[14]The RN was thus faced with designing a carrier that would be survivable under the conditions to be expected in the Atlantic, Mediterranean, and Pacific Oceans, and before the development of effective naval radar; these conflicting demands resulted in the development of aircraft carriers whose decks were armoured against 500 lb armour piercing bombs and 1000 lb general-purpose bombs.
Within the confines of ship design, and the Second London Naval Treaty to which they complied, the Indomitable and Implacable-class carriers had to accept a reduction in hangar heights (to keep the metacentric height within acceptable limits without exceeding the treaty restrictions on overall displacement) and size, and as a result, had some restriction on aircraft types supplied via Lend-Lease.
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".
[23] Yet, even Ark Royal, Britain's newest carrier prior to World War II, never operated close to her theoretical aircraft capacity.
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.
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 USN liaison officer on HMS Indefatigable commented: "When a kamikaze hits a U.S. carrier it means 6 months of repair at Pearl [Harbor].
[31] USS Bunker Hill was severely damaged by pair of kamikaze hits during preparations for an attack on Okinawa which killed 346 men.
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 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.
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.
[20]Paul Silverstone in US warships of World War II notes regarding US carriers that,'vast damage was often caused by suicide planes (Kamikaze) crashing through the wooden flight decks into the hangar below'.
HMS Formidable was an excellent example of this; while she weathered a severe kamikaze hit in 1945 which cratered her deck armour, the hit caused severe internal structural damage and permanently warped the hull[citation needed] (damage worsened in a postwar aircraft-handling accident wherein a Vought Corsair rolled off a lift[citation needed] and raked the hangar deck with 20mm cannon fire, causing a severe fire[citation needed]; but plans to rebuild her as per Victorious were abandoned due to budget cuts, not structural damage,[34] and she lingered in reserve until 1956 before being towed off to the breakers.
The Royal Navy planned to rebuild most of the armoured carriers in the early postwar period: There seems to have been general agreement that the first ship to be modernized should be an Illustrious.
[34]Illustrious suffered a similar battering, especially off of Malta in 1941 when hit by German dive bombers and late in the war was limited to 22 knots (41 km/h) because her centreline shaft was disabled due to accumulated wartime damage;[35] she spent five years as a training and trials carrier (1948–53) and was disposed of in 1954.
Indomitable was completely refit to like-new condition, only to suffer a severe motor spirit explosion on board, which caused "considerable structural and electrical damage to the ship".
The numerous and capacious American yards on the East and West Coasts allowed the US Navy to build and repair carriers at a more leisurely pace while producing ships collectively at a furious rate.
While flight-deck-level armour was eventually adopted by the Americans for the Midway design, the strength deck remained on the hangar level.
Late-life refits to Midway to bulge her hull and improve freeboard instead gave her a dangerously sharp roll, and made flight operations difficult even in moderate seas.
After the war, most of the Essex-class ships were modified with a hurricane bow and in the case of Oriskany the wooden flight deck surface was replaced with aluminium for improved resistance against the blast of jet engines, making them appear to have armoured flight decks, but in fact their armour remained at hangar level.
The supercarriers of the postwar era, starting with the Forrestal class — nearly 200 feet (61 m) longer and 40 feet (12 m) wider in the beam than their World War II counterparts – would eventually be forced to move the strength deck up to the flight deck level as a result of their great size; a shallow hull of those dimensions became too impractical to continue.
