Japan’s Fourth Carrier Division
By Mike Bennighof, Ph.D.
Our Deluxe Edition of Second World War at Sea: Midway includes other operations that took place in the same region (like Pearl Harbor and Wake Island) but it’s centered on the Battle of Midway and looks at a number of possible variations on the battle and campaign, including its aftermath.
The Americans had a slight edge in carrier air power at Midway, but the Japanese actually sent more carrier planes to sea: two light carriers accompanied surface groups steaming well behind the First Air Fleet and played no role in the battle. Two more went northward to attack American bases in the Aleutian Islands in one of the complex operations beloved by Japanese planners.
Those last two carriers and their escort group (two heavy cruisers, three destroyers and an oiler) form the crux of a series of variant scenarios for the main event, the Battle of Midway.
Rear Admiral Kakuji Kakuta’s Carrier Division Four included one of Japan’s oldest carriers, the light carrier Ryujo, and its newest, the converted ocean liner Junyo. They did not have anything near the efficiency of the four big fleet carriers of the First Air Fleet, nor did they carry nearly as many planes. Another light carrier, Zuiho, steamed with the Midway Invasion Force and did not take part in the strikes against the American carriers.
Ryujo had been designed to take advantage of a loophole in the Washington Naval Limitations Agreement that did not count vessels displacing less than 10,000 tons as “aircraft carriers.” By the time she neared completion that loophole had been closed by the subsequent London Naval Treaty and so she received a second hangar deck to increase her air group from 30 to 48 planes.
She went to sea for the Aleutians Operation carrying 33 planes: a dozen A6M2 “Zero” fighters, replacing the older A5M “Claude” she operated in the first months of the war, and 18 B5N “Kate” torpedo bombers. Her small elevators could not accommodate the big D3A1 “Val” dive bomber, and the Kates could only be brought up to the flight deck on the even smaller aft elevator with difficulty. Since Japanese practice insisted on arming and warming up aircraft on the hangar decks, this hampered Ryujo’s efficiency.
The brand-new Junyo had a nominal capacity of 53 planes, with a planned air group of 48 aircraft. She took 33 aircraft on the Aleutians Operation: 18 A6M2 fighters and 15 D3A1 dive bombers. Japanese planners worried that she would not be able to launch torpedo bombers due to her relatively low speed – Japanese carriers did not carry catapults, instead launching their planes directly off the flight deck, counting on the ship’s speed to help create enough lift to help them take flight. However, Junyo later successfully operated torpedo planes in the South Pacific.
Her air group for the Aleutians Operation had been stitched together at the last moment, and she went to sea with only five of her 33 pilots actually assigned to Junyo. The remainder were carrier-qualified fliers from a shore-based fighter squadron and detached pilots on temporary duty from other carriers or training schools. Other than three pilots from the damaged Shokaku, no one seems to have considered giving the new carrier any more of the planes and pilots from the two fleet carriers that missed the operations while in dockyard hands, Zuikaku and Shokaku.
Zuiho had been converted from a fast submarine support ship just before the war, and carried a nominal air group of 30 planes. She operated with the Combined Fleet’s battleships during the first months of the war, shifting to join the close escort for the invasion force during the Midway Operation. She had 24 planes for this mission: six Zero fighters, six of the older A5M “Claude” fighters, and a dozen B5N2 torpedo planes.
Japanese operational doctrine had developed in a seemingly-insane manner over the previous decades, the idea of “keep it simple, stupid” being utterly alien to the Imperial Navy’s way of thinking. The simple principle of concentration of force would call for either Carrier Division Four to operate directly with the First Air Fleet against Midway, or for the 63 planes of its two carriers to be distributed among the four fleet carriers, thereby replenishing their shortfalls.
That did not fit with Japanese doctrine or practice; air groups were considered an integral part of the ship’s company, and were not easily shifted between ships except in emergency circumstances (in practice, during the Battle of Midway the Japanese managed to very effectively integrate aircraft and pilots from their three lost carriers into Hiryu’s strikes against Yorktown).
The Aleutians Operation was not seen as a diversion, but an attack on a separate objective to be carried out simultaneously with the Midway Operation. It seems to have been added at the behest of the Naval Staff, extracting approval for the one operation as the price of internal political support for the other. And so it was inevitable that it would be assigned air cover from second-line carriers, as had been done during operations in the South Pacific and Indian Ocean in the war’s first months.
The moment for Kakuta and his carriers came at the climax of the Battle of Midway, as three of Japan’s four carriers burned out of control along with one of the three American carriers. Of the two surviving American carriers, Hornet’s air group had been devastated in the morning’s air operations, with her torpedo squadron annihilated and her fighter squadron forced to ditch most of its planes.
As Jonathan Parshall and Anthony Tully point out in their Shattered Sword, the obvious move for the remaining Japanese carrier, Hiryu, was to open up more space between her and the American carriers, even as First Air Fleet’s battle cruisers, cruisers and destroyers pressed forward in hopes of a nighttime surface engagement. They did not need the carrier along at that point. Instead Rear Admiral Tamon Yamaguchi kept closing the range to the Americans, who soon enough struck back and sank his remaining flattop. Had he turned northeast after launching his strike against Yorktown, he would have been beyond the range of the American scout planes that found his ship and brought the fatal attacks down on Hiryu.
While Yamaguchi was throwing away First Air Fleet’s last carrier along with his own life, Combined Fleet commander Isoroku Yamamoto had directed Kakuta to break off the attack on the Aleutians and head southward to join up with Yamaguchi. The orders found Kakuta in the midst of a strike against Dutch Harbor, and he could not break it off until his planes had returned and he had re-fueled his ships. Fourth Carrier Division eventually headed south at top speed, only to have the orders cancelled. The two carriers returned to the Aleutians and attacked the American islands once again.
Given a prompt receipt and execution of the re-deployment order, Kakuta still could not have been off Midway for several more days. Once he arrived, First Air Fleet would have Hiryu and four or five light carriers, depending on whether Yamamoto followed through on his initial intent to fling the ancient training carrier Hosho and her handful of biplanes into the fight.
By that point, Hiryu would probably have been operating two dozen planes or less. Junyo and Ryujo had 56 aircraft remaining between them after losing seven planes in the strikes on Dutch Harbor and Zuiho another 24. That would have given Chuichi Nagumo of First Air Fleet – assuming he managed to return from the light cruiser Nagara, where he planned to lead the torpedo attack on the Americans – just under 100 planes. While most organizations would have cashiered Nagumo on the spot for losing three of his four fleet carriers, the Imperial Japanese Navy ultimately kept him in command of First Air Fleet even after its enormous losses were known so he no doubt would have retained his position had the battle extended to another round of carrier strikes.
The Americans probably would have fielded about the same number of planes on their two carriers. Yorktown had been lost, though many of her planes had found homes aboard the other two American flattops. Both Enterprise and Hornet had suffered enormous losses in just one day of fighting, particularly among their torpedo planes, and even with the reinforcements from Yorktown they probably would have been operating about the same number of aircraft.
The “Midway: The Aftermath” scenario section of our Midway Deluxe Edition game puts the fleets in a new situation: no ships have suffered any damage (all of those having sunk), air power is roughly equal, but this time each side knows exactly what the other is doing. The Japanese are still trying to press forward for a landing on Midway Island, which Yamamoto still believed possible after the horrendous losses of the initial carrier battle. The Americans are out to stop them; though Enterprise and Hornet have depleted flight decks are depleted the newly-repaired carrier Saratoga has just arrived at Pearl Harbor with her escorts and a brand-new air group.
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Mike Bennighof is president of Avalanche Press and holds a doctorate in history from Emory University. A Fulbright Scholar and award-winning journalist, he has published over 100 books, games and articles on historical subjects.
He lives in Birmingham, Alabama with his wife, three children and his dog, Leopold. Leopold likes catching lightning bugs.