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Aircraft Carriers


Photograph of Essex-class carrier

National Archives #80-G-68097

The Pacific War was the heyday of the aircraft carrier. Before war broke out, carriers were regarded as an important supporting element for the battle line; by the time the war ended, they effectively were the battle line, displacing battleships as the queens of the fleet. Five major carrier engagements were fought during the war: Coral Sea, Midway, Eastern Solomons, Santa Cruz, and Philippine Sea. By contrast, there were only two battleship engagements: Guadalcanal and Surigao Strait.

Aircraft carriers themselves are nothing but floating airfields. A few of the earliest carriers, converted from battle cruiser hulls under the terms of the naval disarmament treaties, carried 8" (20cm) guns and had substantial armor belts. But most carriers were armed only with dual-purpose and antiaircraft guns, and their armor protection was comparable to that of a cruiser. Their power lay in their air groups, which typically were composed of three to five squadrons of fighters and light bombers, a total of 60 to 90 aircraft. Whereas a battleship could fire shells to a distance of perhaps 30 miles (50 km), and rarely hit a maneuvering target at that distance, the air group of an aircraft carrier could project accurate firepower out as far as 300 miles (500 km). Its aircraft also gave a carrier group a tremendous search area.

Photograph of Helldivers spotted on deck

U.S. Navy. Via ww2db.com

An aircraft carrier had to have a combination of high speed and a long flight deck to operate a large air group.  Carrier commanders thought in terms of the deck load strike, which was the largest group of aircraft that could be assembled on deck and successfully launched in a single operation. Aircraft were spotted (positioned on deck for launch) by the flight deck crew, who manhandled the aircraft into place. On Japanese carriers, fighters and dive bombers were spotted about 30' (9m) apart and torpedo bombers about 33' (10m) apart. By 1943 the Americans had begun taking advantage of the tightly folding wings on their aircraft by spotting aircraft with wings still folded. This permitted more aircraft to be spotted on deck.

Spotting took about 40 minutes on the Japanese carriers of 1941, and another 20 minutes was required to warm up the aircraft engines. In 1943, the Americans began equipping their aircraft carriers with jeeps equipped to hitch to the aircraft and move them more rapidly. Fighters were invariably stationed in front to be launched first, in spite of their lesser endurance, because they required a shorter deck run to get airborne (typically 250' or 76m for a Zero or Wildcat fighter.) American carriers were equipped with catapults to decrease the minimum required run, which allowed them to operate larger groups of heavier aircraft. Japanese carriers also began to be equipped with catapults just before war broke out, starting with the Shokakus.

Photograph of LSO on the carrier Enterprise

National Archives #80-G-17531

It was also necessary to get the aircraft back down after they completed their mission. Just getting back to the carrier could be a problem, since light aircraft navigation was inexact and the carrier itself might have been forced to maneuver away from the expected rendezvous point. American carriers were equipped with the YE-ZB homing system, which used a rotating directional antenna to broadcast a different Morse letter to each of twelve directions away from the carrier. A returning aircraft could determine from the letter being broadcast what its position was relative to the carrier. For security, the code letters were changed every day or sometimes on each mission. The signal was sent on a UHF (ultrahigh frequency) band that could not be received below the horizon, providing some protection from enemy direction finding.

Arrestor wires were used to bring landing aircraft to a quick halt. These were steel cables suspended across the rear half of the flight deck, just above deck level, where they could be caught by a tail hook lowered from the rear fuselage of a carrier aircraft. The arrestor wires were hydraulically loaded so that they offered steady resistance to being pulled forward by the aircraft. Japanese pilots took pride in catching the second wire, which was considered a perfect landing, and which earned the pilot a five yen bonus to his pay. (Normal monthly pay for a Japanese lieutenant was sixty yen per month.)

Photograph of barrier crash

National Archives #80-G-354753

There was also a crash barrier forward of the arrestor wires. This was a strong net about 15 feet high. If the tail hook failed to catch any of the arrestor wires, or if an arrestor wire malfunctioned, the crash barrier prevented the aircraft from rolling into the forward area of the flight deck, where aircraft that had just landed or were about to take off were usually parked. The crash barrier was a last ditch: An aircraft that went into the crash barrier was likely to be damaged, and its crew could easily be injured.

Once an aircraft landed, the crash barrier was lowered and the aircraft taxied forward to make room for the next aircraft to land. Aircraft could then be moved the hangar deck for maintenance, using large deck elevators. Early carriers placed these elevators down the centerline of the flight deck, but beginning with the Wasp, carriers began to be built with elevators on the edges of the flight deck, where they would be less likely to interfere with flight operations if they malfunctioned.

In addition to strikes, aircraft carriers also provided local air defense in the form of a combat air patrol. The combat air patrol consisted of fighters that patrolled over the fleet in order to spot and intercept incoming enemy strikes. The Japanese typically launched shōtai (units of three fighters) at two hour intervals to patrol at an altitude of around 12,000' (3600m). Radio equipment on Japanese fighters was very poor, and individual shōtai simply attacked any enemy aircraft they sighted. American fighters usually operated in divisions of four aircraft, and because their radio equipment was more reliable, they relied more heavily on fighter direction from their carriers. Early in the war, the Americans sometimes supplemented the high altitude fighter patrol with a low altitude antitorpedo bomber patrol, often of dive bombers acting as fighters.

Most Japanese and American carriers could carry more aircraft than they could effectively operate, and the number of aircraft that could be operated also depended on the size of the aircraft. This leads to some ambiguity in the aircraft carrying capacities quoted for aircraft carriers. Unless otherwise noted, the aircraft capacities listed in this encyclopedia are the nominal operating capacities at the time the ship went into war service. Extra aircraft packed onto a carrier complicated damage control, as was the case with Bismarck Sea, lost at Iwo Jima when a single kamikaze struck the vessel while it was overloaded with aircraft transferring personnel from other ships.

Both Japanese and American carriers proved potent but fragile. Their air groups could wreak tremendous damage on the enemy, but the carriers themselves were a highly vulnerable combination of gasoline tanker and munitions ship, albeit with heavy antiaircraft defenses and some armor protection. The Americans greatly improved their damage control techniques during the war, which allowed some carriers (such as the Franklin) to make it home in spite of incredible damage. The Japanese did not improve their damage control as much and continued to lose carriers unnecessarily.

A peculiarity of Japanese carriers was that, whereas Allied carriers used landing signal officers (LSOs) equipped with signaling paddles to guide aircraft in to land, the Japanese carriers used an ingenious system of signal lamps. On each side of the flight deck, a red lamp was mounted thirty to fifty feet aft of a green lamp. A Japanese carrier pilot only needed to aim between the pairs of lights and adjust his glide path so that the red lamps appeared to be just above the green lamps. The system was effective enough that even the poorly trained carrier pilots of 1944 were usually able to get their planes down safely. Its only limitation was that there was no way to signal speed adjustments. The U.S. Navy developed similar systems only after the war ended.

Another difference between Japanese and American carrier design was that the Japanese insisted on refueling and rearming aircraft on the hangar decks. The Americans preferred to refuel and rearm on the flight deck.  Japanese carriers typically had two hangar decks enclosed by the hull, while American carriers typically had a single open hangar deck. The Japanese did not use crash barriers, and, as a result, the flight deck had to be cleared while landing aircraft, and each aircraft had to be struck below as soon as it had landed. As a result, the Japanese had a longer turnaround time for rearming and refueling their aircraft, and any bomb that penetrated a Japanese flight deck exploded in an enclosed and poorly-ventilated space, with the kind of consequences seen at Midway.

Both Japanese and American carriers were designed for a war in which they would operate for prolonged periods far from friendly bases, with their primary target being the other side's carriers. British carriers were designed for a very different war, in which they would be operating close to home in restricted waters under threat from both land-based air and surface forces. British carrier operations were restricted to the Indian Ocean until late 1944, and there was never a carrier battle between the British and the Japanese. This was just as well for the British. British fighter direction was of a very high caliber, and their aircraft carriers had armored flight decks and other features that made them considerably less vulnerable to damage than American or Japanese carriers. This became clear during the Okinawa campaign, when kamikazes hit several British carrier flight decks without putting the ships out of action. Because of the armored flight decks, it was uniquely British practice to strike all aircraft below when air attack was threatened. But the armored decks came at the cost of smaller air groups, and the British carrier punch was further weakened by the miserable quality of British naval aircraft. It was only after the British began using American naval aircraft provided under Lend-Lease that their carriers could operate effectively against the Japanese. Even then, one series of strikes by the British resulted in the loss of 41 aircraft out of 378 sorties.

Allies versus Japan: The Balance Sheet

There are striking similarities between the development of aircraft carriers by Japan and the United States. Both experimented with a single small converted carrier immediately after the First World War, Hosho in the case of the Japanese and Langley for the Americans. Both then converted two capital ship hulls to large carriers in accordance with the naval disarmament treaties, Akagi and Kaga for the Japanese and the Lexingtons for the Americans. Both then experimented unsuccessfully with a "minimum carrier" design, Ryujo for the Japanese and Ranger for the Americans. Both then settled on a larger carrier design, Soryu and its near sister Hiryu for the Japanese and the first two Yorktowns for the Americans. At this point, with the collapse of the treaty structure, the two powers diverged. The Japanese rapidly completed the excellent Shokakus, while the Americans rushed to completion a third Yorktown and another "minimum carrier", Wasp, originally designed to use the remaining displacement allowed under the now-lapsed treaties.

The Japanese and Allied aircraft carrier fleets were fairly balanced at the start of the war. The Japanese had ten aircraft carriers, but only six were first-line carriers capable of operating large air groups. The Americans had seven aircraft carriers, one of which (the Ranger) never served in the Pacific because of its design flaws. The other six were comparable to their Japanese counterparts, but they were committed piecemeal to the Pacific theater because of the priority given to the European war. The British did not have a single carrier in the Far East when war broke out, but had deployed four carriers to Ceylon by 1943 that were roughly equivalent in fighting power to the four Japanese light carriers.

Both sides completed additional carriers during the war, but the Allies had a tremendous advantage in new naval construction. The Japanese completed six fleet carriers, four light carriers, and approximately seven escort carriers during the war. The United States completed seventeen fleet carriers of the Essex class, eleven light carriers of the Independence class, and 77 escort carriers, while the British were able to complete a total of thirteen fleet carriers and 41 escort carriers during the time span of the Pacific War. The Japanese would have been overwhelmed even if they had been able to maintain a unit-for-unit quality advantage.

Though Coral Sea and Santa Cruz were clearly Japanese tactical victories, it can be argued that every one of the carrier battles of the Pacific War was a strategic American victory, since the Japanese failed to attain their objectives while the Americans succeeded, at least marginally. At Coral Sea, the Japanese were forced to call off their Port Moresby invasion, while the Japanese victory at Santa Cruz failed to relieve the Japanese land forces on Guadalcanal. The American victories at Midway and Philippines Sea were decisive both tactically and strategically. Only at Philippines Sea did the Americans have a decisive numerical advantage.

The American ascendancy in carrier combat can be traced to three factors.

Recruitment and training. American naval pilots were elite airmen, though not as good as their Japanese opponents at the start of the war. American naval fighter pilot training emphasized deflection shooting and team tactics, which received less emphasis in the Japanese naval fighter arm. This did much to compensate for greater Japanese combat experience and better Japanese aircraft performance (best exemplified by the Zero) early in the war.

With a population 60% greater than Japan's, and with an automobile culture that encouraged the development of mechanical skills, the Americans had a large pool of potential airmen to draw on. They also adopted rotation policies that supported a training organization capable of turning out large numbers of qualified pilots. The Japanese training system would have been inadequate to keep up with the heavy attrition in the South Pacific campaign even if there had been adequate numbers of young Japanese men with the mechanical aptitude required for air combat. The decrease in Japanese pilot skill became apparent as early as 1943.

Fighter direction. Though American fighter direction was inept in the Battle of the Eastern Solomons, it improved considerably thereafter. The Americans were superior in radar technology, which greatly assisted American fighter direction. In addition, American aircraft radios were much superior to Japanese radios, which were so poor that they were often removed by fighter pilots to save weight. The Americans carefully selected and trained fighter direction officers to work from the flag carrier of a task force and coordinate fighter interceptions. Many were former stockbrokers, who proved to have an aptitude for correlating data and making snap decisions.

The Japanese had neglected fleet air defense prior to war, believing that the best defense was to strike the enemy first and wreck his carrier flight decks. This attitude was slow to change until after the debacle at Midway, where inadequate fighter direction led to the loss of three carriers to American dive bombers in a matter of minutes.

Technology. The American carrier air groups started the war equipped with fighters that were distinctly inferior to their Japanese counterparts. However, by 1944, the Japanese had lost their aircraft performance advantage with the introduction of second-generation Allied aircraft like the Hellcat. Together with the decreasing quality of Japanese pilots, this spelled disaster for the Japanese.

In addition to superior aircraft, the Americans developed superior antiaircraft defenses. American antiaircraft gun directors started out good and steadily got better. The 5"/38 dual-purpose gun was a solid design that was further enhanced with the introduction of the VT radar proximity fuse and radar direction. Air attack on an American carrier task group became an increasingly suicidal activity even for those aircraft that managed to break through the fighter defenses.

Carrier Task Forces


Photograph of carrier task force

National Archives #80-G-278815

Because carriers were a relatively new and untried weapons system, there was much uncertainty on both sides on how they should best be employed. Both sides initially viewed carriers as support units for the battle line, and anticipated that carriers would operate near the battleships during a fleet engagement. However, the Americans had concluded during peacetime maneuvers that the carriers should operate some distance from the battle line, where they would be harder to spot. American battleship commanders complained that the carriers invariably fought their own private war against each other rather than supporting the battleships as they ought; King replied that if the carriers did not first engage the enemy carriers, there would be no air support to be had. This reflected one of the early lessons of the Second World War, which is that command of the air was usually a prerequisite to success in land or sea engagements.

The organization of 1 Air Fleet on 10 April 1941 reflected a willingness by at least some Japanese naval leaders to mass their carriers as a single independent strike force. The Americans experimented with carrier task forces composed of a single carrier screened by cruisers and destroyers.  The two approaches reflected one of the unanswered questions tacticians wrestled with early in the war, namely, should carriers be massed? It is normally considered good tactics to mass firepower to avoid risking defeat in detail, but the vulnerability of carriers to air attack led American tacticians to be wary of putting all their eggs in one basket. The disaster at Midway suggested that the Americans had the better argument, but the relatively small number of carriers involved (three for the Americans, four for the Japanese) left considerable uncertainty.

By March 1943 the Americans had concluded that the ideal was two carriers per task force, with the task forces concentrating for strikes and separating by at least 25 miles when air attack seemed imminent. The ideal screen was 20 to 24 destroyers and either six heavy cruisers, or two battleships and four antiaircraft cruisers. The destroyers were stationed in a circle at a radius of 1500 to 2500 yards from the center of the task force, with the heavier warships stationed closer to the carriers. In practice, there were simply not enough screening vessels for such extravagant protection, and most task groups consisted of three or four heavy or light carriers protected by fewer heavy warships and much fewer destroyers than the ideal. For example, Task Group 50.1 at Tarawa had two fleet and one light carrier screened by five heavy cruisers, one antiaircraft cruiser, and just eight destroyers.

By this point in the war, Japanese practice was not much different than American at the task force level. However, the Japanese often kept their task forces much more widely separated than the Americans. This was in part a move of desperation: Task forces containing less capable light carriers were often employed in a manner that suggests they were viewed as sacrificial decoys. However, a tendency to have widely separated forces converge on the objective had characterized Japanese tactical thinking from the very beginning of the war.

Air Groups


Photograph of air group warming up for launch

National Archives #80-G-41686

American fleet carriers typically carried four squadrons of 18 planes each. At the start of the war, these were a scout squadron, a bomber squadron, a torpedo squadron, and a fighter squadron. The scout squadron flew the same model of dive bombers as the bomber squadron and usually functioned as a second bomber squadron when it was not performing its scouting role. The Battle of the Coral Sea convinced the Americans that more fighters were required, and the fighter squadron was increased to 24 aircraft. After Midway, the fighter contingent was increased to two squadrons of 18 or 19 fighters, the approximate limit of what the fleet carriers of 1942 could operate. The authorized air group for most U.S. fleet carriers thus became 36 fighters, 36 dive bombers, and 16 torpedo bombers in July 1942.

At about the same time, the commander of Task Force 17 (Hornet), George Murray, and the captain of the Hornet, Charles Mason, developed a set of deck load strike plans based on war experience. The fighters were organized into flights of eight aircraft, the first for combat air patrol, the second spotted on the flight deck with the first deck load strike, the third in the hangar with the second deck load, and the fourth as reserve combat air patrol. This increased flexibility and reduced the time required to launch a strike.

As the war progressed, it was found that there was little a dive bomber could do that fighters or torpedo bombers could not do as well. The two dive bomber squadrons were reduced to 14 planes each in late 1943 and then to a single squadron of 15 planes by late 1944. The number of torpedo bombers remained roughly constant as the number of fighters was increased. With the growing kamikaze threat, fleet carriers began to ship as many fighters as could be squeezed on board -- up to 70 on an Essex, with the dive bomber and torpedo bomber contingents reduced to just one squadron each of 15 planes. The Essexes were designed to carry a fifth reserve squadron, but this promptly became an operational fighter squadron.

Japanese fleet carrier air groups consisted of a squadron each of dive bombers, fighters, and torpedo bombers. These typically had 15 to 27 planes, depending on the operating capacity of the carrier.  (Unlike American carrier air groups, each Japanese carrier air group was permanently assigned to a particular carrier.)  Japanese air groups increased slightly in size and included somewhat more fighters as the war progressed, but the Japanese failure to adopt deck stowage of aircraft prevented their carrier air groups from reaching the size of their American counterparts. The Japanese were also hindered by the design of the folding wings on their aircraft, especially on the dive bombers, which could fold up little more than the wing tips.

An important advantage held by the Japanese until 1943 was their proficiency at coordinating air groups from separate carriers into a single massive strike. The Americans did not begin to master this technique until 1943, and the carrier battles of 1942 were characterized by uncoordinated strikes by relatively small groups of U.S. aircraft.

A typical British air group in 1942 was composed of just 12 to 30 fighters and 12 to 24 torpedo bombers. Dive bombers were not carried until 1943.

Carrier Aircraft

When war broke out, it was accepted by most advocates of air power that carrier aircraft could not hope to match the performance of land-based aircraft. Carrier aircraft had to have sturdy undercarriages for hard landings on a flight deck, which added to their complexity and weight. They also had to have a low stall speed to allow takeoffs and landings from a short deck, which implied a low wing loading that restricted their performance. However, the Japanese Navy refused to accept the conventional wisdom, and the A6M "Zero" proved to be a carrier fighter with formidable performance. This was possible in part because of Japanese fighter design philosophy, which emphasized speed, range, and maneuverability at the expense of sturdiness and protection. It was less challenging to produce a light (almost flimsy) carrier fighter that emphasized the former rather than the latter.

The lighter construction of Japanese carrier aircraft also gave them a range advantage. At the start of the war, a coordinated American carrier strike had a maximum radius of 175 miles (280 km), the maximum practical operating radius of its F4F Wildcats and TBD Devastators. The Japanese could launch a coordinated strike from well over 200 miles (320 km), as they demonstrated at Pearl Harbor, where they launched their strikes from 210 miles north of Oahu. Following the battle of Midway, the Wildcats began carrying belly tanks that extended their range, and the Devastator was replaced with the superior TBF Avenger. This increased the range of a coordinated American carrier strike to well over 200 miles, and at the Battle of the Philippine Sea, a strike of Avengers, F6F Hellcats, and SB2C Helldivers was launched against a Japanese carrier force thought to be 275 miles (440 km) distant. However, the Japanese strike radius also increased over time, so that the Americans never really caught up.

Coordinated strikes were also made more difficult for the Americans by the different cruising speeds of the aircraft, ranging from 128 mph (206 km/h) for the Devastators to 161 mph (259 km/h) for the Wildcats. By contrast, the Japanese had been more careful to match the cruising speeds and ranges of their Zeros, D3A "Vals", and B5N "Kates", with cruising speeds ranging from 161 mph (259 km/h) for the Kates to 207 mph (333 km/h) for the Zeros. The Zeros and Vals in particular were very closely matched in range and cruising speed. With the introduction of the Avenger, the disparity in American cruising speeds was eased significantly and strikes became correspondingly easier to coordinate.

Historical Perspective

It is notable that history has seen only five carrier battles, all during the Pacific War between the Japanese and the Americans. Carrier combat was a unique feature of that war, unlikely to ever be repeated. Each battle lasted only two or three days, during which both sides experienced heavy losses in their carrier air groups, necessitating the withdrawal of at least part of their surviving carrier forces. Yet the possibility that the enemy might commit his carriers always had to be taken into account when planning operations, which accounts for the dominance of these ships in the Pacific War.

Carrier categories

Fleet Carriers

Light Carriers

Escort Carriers


References

Bergerud (2000)

Dunnigan and Nofi (1988)

Evans and Peattie (1997)

Friedman (1983, 2004, 2013)

Hastings (2007)

Larrabee (1987)

Lawson and Tillman (1996)

Lundstrom (2006)

Peattie (2001)

Proc (2012-1-14; accessed 2012-3-9)

Stern (2010)

Tillman (2005)

Werneth (2008)

Woolridge (1993)

Zimm (2011)



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