The Japanese Carrier Force in WWII (1941-1945)

Kaga and Hosho at anchor prior to the Second World War

Japan entered the Second World War with a force of ten carriers, while the United States and Great Britain each had seven. However, four of the Japanese ships were light carriers while all seven American ships were fleet carriers, meaning that despite the difference in numbers both carrier forces could accommodate roughly 600 aircraft. In Britain's case all seven of her ships were light carriers and could only accommodate a total of less than 300 aircraft.

Japanese Carrier Force 12/1941 (capacity of 600 aircraft):

Hosho - 168 meters, 25 knots, 20 aircraft
Akagi - 261 meters, 31 knots, 90 aircraft (battlecruiser hull)
Kaga - 248 meters, 28 knots, 90 aircraft (battleship hull)
Ryujo - 180 meters, 29 knots, 40 aircraft
Soryu - 228 meters, 34 knots, 70 aircraft
Hiryu - 227 meters, 34 knots, 70 aircraft
Zuiho - 217 meters, 28 knots, 30 aircraft (converted submarine tender)
Shokaku - 258 meters, 34 knots, 80 aircraft
Zuikaku - 258 meters, 34 knots, 80 aircraft
Shoho - 217 meters, 28 knots, 30 aircraft (converted submarine tender)

The last three of these ships (Shokaku, Zuikaku, and Shoho) were brand new, having commissioned in August, September, and November of 1941. Zuiho was also rather new, having commissioned exactly a year before in December of 1940. It was this sudden spate of construction (combined with Britain's loss of four carriers against Germany) that gave Japan the world's largest carrier fleet when she entered the war.

However, while Japan had prepared for war, she had not prepared for a long war and in December 1941 there was no sign of a sustained building program to replace combat losses. Although two liners (Junyo and Hiyo) and one submarine tender (Ryuho) were in the process of being converted to light carriers, only a single new fleet carrier (Taiho) was under construction. Even more strangely, Taiho was not a continuation of the successful Shokaku-class, but a radical new armored design. In contrast, the United States had no fewer than five fleet carriers already under construction when the war began and rapidly ordered many more after hostilities were declared.

Shoho, the first Japanese carrier to be lost.

In May 1942 the Japanese carrier force suffered its first loss when the light carrier Shoho was sunk during the Battle of the Coral Sea. However, losing this converted submarines tender was of little importance, especially since the more capable Junyo had commissioned just a few days prior to the battle. The fleet carrier Shokaku also suffered damage that put her out of action until June 1942, but this damage had a minimal effect on Japanese planning.

However, June 1942 spelled disaster as the Battle of Midway saw four of Japan’s six fleet carriers (Akagi, Kaga, Soryu, and Hiryu) sent to the bottom. Still, it should be noted that American losses at Coral Sea and Midway meant that Japan still had the larger carrier force - six ships to five. Japanese preparations also paid off again as Hiyo joined the fleet in July 1942, while the United States had yet to complete any new carriers. But even though the United States had fewer carriers, they were all fleet carriers while the Japanese force was now almost entirely light carriers. This meant that the overall capacity of the American force was now noticeably higher at roughly 420 aircraft to 350.

Japanese Carrier Force 08/1942 (capacity of 350 aircraft):

Hosho - 168 meters, 25 knots, 20 aircraft
Ryujo - 180 meters, 29 knots, 40 aircraft
Zuiho - 217 meters, 28 knots, 30 aircraft (converted submarine tender)
Shokaku - 258 meters, 34 knots, 80 aircraft
Zuikaku - 258 meters, 34 knots, 80 aircraft
Junyo - 219 meters, 25 knots, 50 aircraft (converted liner)
Hiyo - 219 meters, 25 knots, 50 aircraft (converted liner)

Japan was given no time to recover her strength as the next month (August 1942) the United States launched an offensive against Guadalcanal, leading to the Battle of the Eastern Solomons in which Ryujo (arguably the best of the light carriers) was lost. This action was quickly following in October 1942 by the Battle of Santa Cruz. Although no further Japanese carriers were sunk in this second battle, Shokaku and Zuiho both suffered damage that put them out of action for months.

Although the converted submarine tender Ryuho commissioned in November 1942, when the one year anniversary of the Pearl Harbor attack arrived, the Japanese carrier force was a shadow of its former self. Of its seven ships, only five were operational and only one of those five was a fleet carrier. While its nominal capacity of 340 aircraft was already just over half of what it had boasted one year before, its actual capacity was down to only 230 aircraft. Finally, in a stroke of bad luck, Ryuho was damaged by a submarine torpedo in early December 1942. Thus, when 1943 began, the Japanese carrier force had just four operational ships with a total capacity of only 200 aircraft.

Japanese Carrier Force 12/1942 (capacity of 340 aircraft):

Hosho - 168 meters, 25 knots, 20 aircraft
Zuiho - 217 meters, 28 knots, 30 aircraft (converted submarine tender)
Shokaku - 258 meters, 34 knots, 80 aircraft

Zuikaku - 258 meters, 34 knots, 80 aircraft

Junyo - 219 meters, 25 knots, 50 aircraft (converted liner hull)

Hiyo - 219 meters, 25 knots, 50 aircraft (converted liner)

Ryuho - 216 meters, 26 knots, 30 aircraft (converted submarine tender)

Amazingly, it was only at this point, a year after the war had begun and half a year after the disaster at Midway, that Japan began work on constructing new carriers. Of course, shipbuilding does not take place quickly and waiting for new ships meant that the Japanese carrier force was unable to influence the war from late 1942 until mid 1944. And while the Japanese carriers did not engage the United States Navy directly during this time, they were still being hunted by American submarines. Although no carriers were lost, Hiyo was torpedoed in June 1943 and Junyo was torpedoed in November 1943, with both carriers requiring several months of repairs.

The first of the new Japanese carriers were conversions of the two seaplane tenders Chitose and Chiyoda, which began in January 1943. However, the real effort began in August 1943, when the keel was laid for Unryu, the first in what was planned to be a class of sixteen new fleet carriers. But while Japan was beginning work on its new carriers, the United States was completing the ships it had started before the war began. By December 1943, the Japanese carrier force had only added the converted light carriers Chitose and Chiyoda. In contrast, the American carrier force had seen no fewer than seven Essex-class fleet carriers and nine Independence-class light carriers join its ranks. By the time Taiho finally commissioned in March 1944, an eighth Essex-class ship had been completed.

Japanese Carrier Force 06/1944 (capacity of 480 aircraft):

Hosho - 168 meters, 25 knots, 20 aircraft

Zuiho - 217 meters, 28 knots, 30 aircraft (converted submarine tender)

Shokaku - 258 meters, 34 knots, 80 aircraft

Zuikaku - 258 meters, 34 knots, 80 aircraft

Junyo - 219 meters, 25 knots, 50 aircraft (converted liner)

Hiyo - 219 meters, 25 knots, 50 aircraft (converted liner)

Ryuho - 216 meters, 26 knots, 30 aircraft (converted submarine tender)

Chitose - 192 meters, 29 knots, 30 aircraft (converted seaplane tender)

Chiyoda - 192 meters, 29 knots, 30 aircraft (converted seaplane tender)

Taiho - 261 meters, 33 knots, 80 aircraft

But by this point the United States was approaching the Philippine Islands and Japan had little choice but to counter attack in what became the Battle of the Philippine Sea in June 1944. The results of this lopsided engagement were to be expected - a complete defeat in which Japan lost three carriers (Shokaku, Hiyo, and Taiho) and had three more (Zuikaku, Junyo, and Chiyoda) badly damaged. These losses again gutted the Japanese carrier fleet - of its three fleet carriers, two were sunk and one was damaged. Further, of its two largest light carriers, one was sunk and the other damaged.

However, the first two Unryu-class fleet carriers (Unryu and Amagi) commissioned in August 1944, quickly replacing Shokaku and Taiho, and all three damaged carriers were also promptly returned to service. But while Japan's belated carrier construction program was finally paying off, the Japanese Navy had run out of aircraft and pilots to equip its new ships.

Japanese Carrier Force 10/1944 (capacity of 390 aircraft):

Hosho - 168 meters, 25 knots, 20 aircraft

Zuiho - 217 meters, 28 knots, 30 aircraft (converted submarine tender)

Zuikaku - 258 meters, 34 knots, 80 aircraft

Junyo - 219 meters, 25 knots, 50 aircraft (converted liner)

Ryuho - 216 meters, 26 knots, 30 aircraft (converted submarine tender)

Chitose - 192 meters, 29 knots, 30 aircraft (converted seaplane tender)

Chiyoda - 192 meters, 29 knots, 30 aircraft (converted seaplane tender)

Unryu - 227 meters, 34 knots, 60 aircraft

Amagi - 227 meters, 34 knots, 60 aircraft

For its final sortie in the Battle of Leyte Gulf in October 1944, the carrier force would serve only as a diversion as it no longer had enough aircraft for serious combat. Bravely filling this role resulted in the loss of Zuikaku, Zuiho, Chitose, and Chiyoda. Now the only remaining member of the pre-war fleet was Hosho, which had served as a training carrier since Midway. However, even if the aircraft had existed, there was no hope that Japanese carrier force could oppose the American fleet, which by this point consisted of no less than twenty three carriers. 

Although the third Unryu-class carrier (Katsuragi) had also commissioned a week before the Battle of Leyte Gulf, none of the three new fleet carriers took part in the battle. In November the converted Yamato-class battleship Shinano (266 meters, 27 knots, 50 aircraft) became the the last Japanese carrier to be built, temporarily bringing the fleet up to seven carriers before she was sunk by an American submarine on her maiden voyage in the same month.

The loss of Shinano marked the beginning of the rapid disintegration of the Japanese carrier force. The next month (December 1944), Unryu and Junyo were both torpedoed, and although Junyo survived her damage was never repaired. Three months later in March 1945, Ryuho, Amagi, and Katsuragi were damaged by air attacks while at anchor, with Ryuho sinking. Amagi was sunk in a follow up attack in April 1945, in which Katsuragi also received heavy damage.

When the war ended in August 1945, only Hosho, Japan's very first carrier, remained operational. Although bomb damage prevented air operations, Katsuragi was also still seaworthy and joined Hosho in transporting Japanese soldiers home from around the Pacific.

Hosho, the only Japanese carrier to survive the entire war intact

When the war began the Japanese carrier force was arguably the strongest in the world. The Japanese Navy's conversion of tenders and liners to light carriers had enabled it to leapfrog the United States Navy in the run up to war despite having an inferior shipbuilding industry and allowed Japan to replace some of its combat losses during the crucial first year of fighting.

What Went Wrong?

First, the disaster at Midway. If Japan had not suffered such massive losses there, it becomes difficult to imagine how the Solomon Islands Campaign could have been a success for the United States. Historically, it was already a very close affair and if Japan had four more fleet carriers then it is quite possible the United States would simply have been overwhelmed and forced to retreat (if the operation had even been begun in the first place).

Avoiding the losses at Midway is also not a particularly unreasonable change - sinking four carriers at the cost one was not a typical American performance during the early war and just a few minor events occurring differently could have easily resulted in a much less decisive result (perhaps a one for one trade as was common in the early battles). Further, the entire Midway plan was dubious from start and the operation should probably have never happened.

Second, the pause in major carrier operations after the October 1942 Battle of Santa Cruz. At this point the Japanese carrier force had been badly damaged and was down to just six ships. However, the American carrier force was actually in far worse shape as, unlike the Japanese, it had not received any reinforcements since the war began and was down to just three ships. Further, Japan still had one more carrier conversion that was about to be completed.

With the Essex-class and Independence-class carriers about to start commissioning in early 1943, this was the last window in which Japan could expect to have numerical superiority and it should not have been squandered. Additionally the United States was overextended and trying to conduct an offensive with limited resources against prepared Japanese positions. If the Japanese Navy had gone all-in during the Solomons Campaign and secured a victory, it is quite possible that they could have ended American offensive operations for a year or more.

Third, the pause in carrier construction from late 1942 to late 1943. Even if the Japanese Navy had been successful in the Solomons, its lack of new carriers during this one year window would still have doomed it to a predictable defeat at the hands of the far more numerous United States Navy. However, this pause was likely not inevitable - when Japan did finally start building carriers again, she actually did remarkably well given her limited resources. If Chitose, Chiyoda, and the Unryu-class had started commissioning a year earlier it would have completely altered the balance of power.

Combined with fewer losses at Midway and a more aggressive defense of the Solomons, this could very well have allowed the Japanese Navy to stick with the United States Navy in terms of carrier numbers into 1944 rather than being hopelessly outmatched in 1943. Of course, the Japanese carriers would still be individually inferior and equipped with less advanced aircraft, but one-sided battles such as the Philippine Sea and Leyte Gulf should not have occurred.

Now, even with such a strategy formulated with the benefits of hindsight, Japan still did not have a clear path to victory. She still had no way of matching American economic output and would have eventually been overwhelmed. However, barring an incredible tactical success, American numbers would likely not have become irresistible until 1945 and it is possible the war would have dragged on until 1947. In such a case, a negotiated peace may have even become possible (of course, the other possibility is that after 1945 the United States begins employing nuclear weapons against Japanese land and naval forces, leading to a rapid victory).

Japanese vs American carrier forces by month (calculated at the 1st of each month) and showing the major carrier battles