What if the Japanese had not attacked Pearl Harbor?
The operational use of Japanese Naval Aviation was designed around the IJN's strategic and operational plan to respond to a US Navy thrust to the Philippines and force a decisive battle on Japanese terms.
The IJN recognized the US Navy as its primary foe from the end of the Russo-Japanese War. From 1906, the IJN began to craft a strategic and operational plan for countering a US Navy thrust into the Western Pacific. Japan's naval building program was designed around the operational and tactical needs for executing the Plan. From what we know now, the IJN was reasonably informed about US Navy strategic concepts for a war in the Pacific. Whether they knew the details or not, or anything about the constant swings of power between the "thrusters", desiring an immediate all-out thrust to the Philippines at the start of a war and the "cautionaries", who sought a deliberate, step by step offensive to Japan is probably moot. The US navy would come west and the IJN had to be prepared to stop them.
Japanese scenarios start with an attack on US possessions and forces in the western Pacific, with or without a declaration of war. They then expected the US Navy to mount an expedition, sooner or later, to relieve or recover the Philippines. With the acquisition of the Mandates, the IJN planned to enmesh the US Navy within the Mandates in a campaign of attrition by Japanese light forces. When the American force had been sufficiently weakened, the Battle Force would sail from the Sea of Japan and execute the "coup de grace".
By the 1930's, the IJN envisioned its light forces as consisting of land based aviation, carrier based aviation, heavy and light cruisers, destroyers and submarines, along with some special systems "cooked up" especially for this campaign. Submarines and seaplanes would make the initial contact. They would shadow the US force and guide other submarines and the land based aviation to the target. The submarines would begin to probe the US perimeter to distract US forces from the oncoming bombers and torpedo planes. The submarines would also scatter mines and miniature subs in the US force's path. At night, Japanese cruisers and destroyers would conduct long-range torpedo attacks with "Long Lances". The Japanese built special torpedo cruisers with 40 tubes installed quick reload gear for torpedoes on their cruisers and destroyers and practiced hard at these tactics.
Once the US forces had been ground down, many ships damaged, the crews exhausted, the Japanese carriers would strike. Up to 1941, the IJN planned to use their CVs in single carrier task forces. Thanks to Genda, the IJN developed a new doctrine and concentrated their carriers into a single strike force. They would have struck at dawn, 4-6 CVs, dive-bombers, torpedo bombers and fighters. The fighters would have swept the skies over the Americans, and the strike forces would have concentrated initially on the US CVs. Once the US naval aviation was broken and air superiority secured, denying use of the skies by the US observation planes and securing its use by the Japanese, the battleships would come forward, and using aerial spotting engage in a long range gunnery duel. Once the culminating point was reached, the Battle Force would close in on and destroy the Americans.
Meanwhile, the subs would be eliminating any wounded vessels, which left formation and tried to reach US ports. With the US forces broken, the remaining IJN light forces, including the carriers and battle cruisers would pursue and complete the enemy's destruction.
How much the US Navy knew about this plan is not entirely known. But US attaches had divined most of the outline of this plan. Whether this had any impact on the change over from a "immediate offensive" to a more cautious approach is also unproven. But the intent of the "thrusters" to charge forward to the Philippines would have played into the IJN's hands. The more cautious approach of "nibbling" through the Japanese defenses was more realistic in its appraisal of both the US and Imperial Japanese Navies.
Anyone who reads "War Plan Orange" can see the development of both navies' strategic plans. More importantly, these plans both reveal the very important place of aviation in the concepts. Both land and carrier based aviation was neither neglected nor ignored. As early as the 1920's, the USN incorporated air power in its "island-hopping" campaign, sought to use seaplane bombers to reinforce the Fleet, developed a plan to convert fast liners and cargo vessels into auxiliary carriers and developed an "end game" to Plan Orange that seized islands off Japan for bases to conduct a strategic bombing campaign.
But the IJN did attack Pearl Harbor. And I would contend that this operational decision was in line with current IJN doctrine. Most IJN staff and commanders saw the carriers as part of the "light forces" dedicated to attrition and pursuit of a US Fleet. Many considered them expendable if the exchange rate was right. As it was, losses were expected by the IJN in its attack and the destruction or disablement of the US Fleet was worth 2-4 fleet carriers. The use a the carrier strike force at Pearl Harbor merely pushed the forward area of the IJN's "prepared" battlefield from the Mandates to the enemy's base. Attrition would commence at Hawaii rather than Wotje or Makin or Saipan. If the carrier strike force had been less successful at Pearl Harbor, the IJN would still have executed its operational plan, when the US fleet struck back after it recovered and reorganized.
As it was, the IJN strike was operationally unsuccessful in one way. US losses at sea in the Mandates would have been unrecoverable. US losses at its Fleet Base were repaired and modernized and brought forward to battle on US terms. The Kido Butai would not have missed its chance at Halsey and the US carriers in the Mandates as it did at Pearl Harbor. Another point is that the US raids early in 1942 on the IJN's Mandates bases showed the difficulty of the IJN to concentrate against raids without a strategic reconnaissance and warning system. While the discredited "thrusters" offensive would have allowed the IJN to concentrate against the USN, the "cautionary" plan would allow the USN to pick the time and place of its offensive and concentrate its own forces at IJN weak points. The IJN operational plan was dependent on ambushing a rash enemy, but gave up the initiative and spread forces across a "cordon" defense. The bottom line, however, as has been pointed out before, is that the IJN could have sunk the entire US fleet available on December 1941 and still faced an overwhelming opponent by 1945.
- 4 March 2000