The Pacific War [7 December 1941 – 2 September 1945] between the Imperial Japanese Navy (IJN) and the United States Navy (USN) is mainly remembered for its aircraft carrier actions. In fact, the aircraft carrier balance was to decide the fate of the conflict. During the first six months of the Pacific War, the IJN wreaked havoc in the southwestern Pacific and the Indian Ocean. It was only after the Battle of Midway [June 1942] that the Japanese lost the initiative in the Pacific and were forced to take a defensive posture. At Midway, the USN inflicted a critical blow to the IJN, sinking four of its fleet carriers.
From this point onwards, the Americans took initiative and started to build-up their carrier force before leapfrogging towards the Japanese home islands. However, before the war, both navies believed that the outcome of the conflict would be decided by a gigantic clash of battleships. In fact, the role and capabilities of the aircraft carrier were still unclear and veteran officers of both the navies were strongly attached to their battleships. The rise of the aircraft carrier in favor of the good old battlewagons proved to be a complicated issue to manage.
This article by Yann Menetrey from Switzerland, a guest author for Defencyclopedia, will cover the development of the aircraft carrier during the Inter-war period in both the IJN and USN and will try to offer a comparison between aircraft carrier doctrines and designs on both sides.
DEVELOPMENT OF AIRCRAFT CARRIERS
Both the United States and Japan had to keep the carrier construction within the constraints of the 1922 Washington Naval Treaty (It was a treaty among the major nations that had won World War I, which agreed to prevent an arms race by limiting naval construction). However, the USN was permitted 135,000 tons of aircraft carriers while the IJN was only allowed 81,000 tons. Interestingly, the two navies shared a similar design progression. Both started with an experimental carrier, serving as technology demonstrators,to gain experience. They were progressively followed by improved designs.
- 1922 ⇒ The USN had commissioned the USS Langley (CV-1), in March, but it was a conversion from the collier USS Jupiter (AC-3).
- 1922 ⇒ The IJN commissioned the Hōshō, the world’s first ship designed and built as an aircraft carrier from the onset, in December.
The Hōshō and the Langley were small ships with a limited air group, displacing 9,500 and 13,900 tons respectively. Next came the first fleet carriers, all being conversions from capital ships.
- 1927 ⇒ The IJN commissioned the Akagi
- 1927 ⇒ The USN commissioned USS Lexington (CV-2) & USS Saratoga (CV-3)
- 1928 ⇒ The IJN commissioned the Kaga
All of them were built on the hulls of battlecruisers (except for Kaga which was a battleship) canceled under the 1922 Washington Naval Treaty.
As the function and the place relative to the battle line of the carrier were still uncertain, both American and Japanese carriers received heavy cruiser caliber guns for defense against cruisers and destroyers. This was followed unique units to mature the aircraft carrier technology. In
- 1931 ⇒ The IJN commissioned the Ryūjō, a light aircraft carrier built to exploit a loophole in the Washington Naval Treaty. In fact, the treaty stated that carriers under 10,000 tons weren’t regarded as “aircraft carriers”.
- 1934 ⇒ The USS Ranger (CV-4) was commissioned and was the first American carrier built and designed as an aircraft carrier from the start.
Japan then built two additional fleet carriers, the Sōryū and the Hiryū. The Japanese further improved their technology with these two ships and reached a “standard design” that would be re-used later during the war with the Unryū-class. Finally, both navies’ carrier technology pinnacled with a well balanced and more sophisticated design: the Shōkaku-class for the IJN and the Yorktown-class for the USN.
DESIGN & DOCTRINE
IMPERIAL JAPANESE NAVY
In the early 1930s, the IJN understood that aircraft carriers, which were at first built to provide air cover, reconnaissance and anti-submarine patrols to the main battle fleet, were, in fact, viable striking platforms in their own right. Thus, the new main target of Japanese carriers was the enemy’s carriers, as their destruction would then allow the IJN to weaken the enemy battle fleet. For the Japanese, the essential precondition for carrier combat was that the IJN strike first. This explains the Japanese emphasis on having large air groups made of light aircraft which gave them a superior striking range, an advantage the IJN kept until 1943.
In general, Japanese carrier design stressed speed and aircraft capacity as they were seen as purely offensive weapons. As a result, the Sōryū and the Hiryū were lightly built and couldn’t take much damage. Unlike the Americans, aircraft capacity was determined solely by hangar space and not all Japanese aircraft had folding wings. Thus, Japanese carriers did not usually possess the aircraft capacity of their American counterparts.
Their air group was composed of three squadrons : a fighter squadron, a dive bomber squadron, and a torpedo bomber squadron. Overall, their capacity to take damage and the ability of the damage control crews to address battle damage was not up to the USN standards, as the IJN expected to strike first and eliminate the threat before it could counterattack. However, the Shōkaku-class represented a major change in Japanese carrier design. No longer restricted by the Washington Naval Treaty which had expired in December 1936, Japan sought for the “perfect carrier”.
The Shōkaku-class had to sport the best of every previous Japanese carrier : the large air groups of the Akagi and Kaga, the range and the speed of the Hiryū, a powerful defensive armament, and better protection. The standard long-range air defense weapon of Japanese carriers was the Type 89 127mm (5in) cannon. The inadequate Type 96 25mm cannon serveed in the immediate and short-range anti-aircraft defense role. Unlike the Americans, the Japanese laid great emphasis on the aerodynamic nature of their carriers. The funnels diverted the hot gasses to the sides and islands were made as small as possible, all this to avoid turbulence for the landing aircraft to the maximum possible extent.
To achieve a quick destruction of the enemy, the Japanese immediately assembled their carriers into divisions (often composed of two carriers) capable of launching massive strikes. The concentration of force proved to be an extremely effective decision and explains why the IJN had the most advanced and powerful carrier fleet in the world by 1939. Typically, when a multicarrier operation was conducted, each carrier would launch either its full dive bomber or torpedo plane squadron with the entire strike being composed of a balance of aircraft type from different carriers. The another strike squadron not committed was retained for a second wave or in reserve. In result, the IJN was able to fully integrate operations from different carriers, far better than the USN or Royal Navy, and achieved a higher level of coordination. Japan’s ability to mass carrier airpower into large striking forces was revolutionary and one important advantage at the start of the war.
UNITED STATES NAVY
The USN had a significant advantage over the IJN, as it was permitted a larger tonnage of carriers. This meant that American carriers could be bigger and carry more aircraft. They had to be fast enough for fleet operations, to escape attack by enemy cruisers and to conduct flight operations in all kinds of wind conditions. Underwater protection was adequate, while the main deck (the hangar deck, not the flight deck) could withstand hits from aerial bombs.
At first, the primary task of the American aircraft carriers was to support the main battle fleet. At this stage, the USN doctrine was more defensive compared to the IJN doctrine, as carriers were expected to protect the airspace over their own fleet and deny the enemy’s strike range advantage. For self-defense, USN carriers were especially well equipped with anti-aircraft guns. The excellent Dual-Purpose 127mm (5in) gun for long-range air defense, the intermediate-range 40mm gun, and the short range 0.50cal (12.7mm) machine guns, later replaced by the Oerlikon 20mm cannon.
At first, American carriers were operating with their escort and cooperation between them was poor. But gradually, the vulnerability of carriers became obvious and the USN developed the carrier’s role into an independent offensive platform, able to operate without the main battle fleet.
From this point, the primary task of the carriers was to destroy opposing carriers as soon as possible, thus preventing their own destruction and setting the stage for intensive attacks on the enemy battle fleet. To maximize the striking power of its carriers, standard USN doctrine called for the launch of an entire air group at one time. American air groups were composed of four squadrons :
- One fighter squadron
- One torpedo bomber squadron
- One dive bomber squadron and
- One scout squadron which could also be used in dive bombing attacks.
In order to quickly launch an entire deck load strike, it was necessary to have the entire strike spotted on the flight deck. U.S. carrier design was shaped by this continuous requirement to quickly generate offensive power. The standing practice called for most of the carrier’s aircraft to be parked on the flight deck, with the hangar deck being used for aircraft maintenance and storage. Open and unarmored hangars facilitated quick launch and could void a bomb explosion, reducing the damage inflicted to the structure of the ship. American carriers were strongly built and the USN put a high priority on damage control. This meant they could withstand significant damage, which can be attested by their combat record.
Generally speaking, at the outbreak of the Pacific War, American carriers were heavier, bigger and sturdier than their Japanese counterparts, although slightly slower. Americans operated larger air groups than their Japanese counterparts. If they could launch bigger air groups, they were incapable, at first, to effectively coordinate their actions. But they had an important advantage in the form of an air search radar, the CXAM-1, introduced in 1941. However, the Japanese had better aircraft, especially in the fighter and torpedo bomber department. Japanese carriers were capable of striking a target 560km (350mi) away with all their aircraft types. On the other end, the Americans could only strike 240km (150mi) away with all their aircraft types, 280km (175mi) without torpedo bombers and 400km (250mi) with dive bombers only.
Also, Japanese aircrews were an elite, better trained, with combat experience from the Second Sino-Japanese War and using better tactics But crew from both sides proved their value and the initial doctrine superiority of the IJN was quickly matched, and later canceled, by American industrial capacity and the USN’s quick adaptation capability.
About the Author
Yann Menetrey is a 21 years old university student living in Geneva, Switzerland. Fascinated by aviation since childhood, and later by military history, he’s running @the_ww2_gallery since three years, an Instagram account dedicated to the Second World War.
Edited and formatted by N.R.P
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