The was a naval strategy adopted by the Imperial Japanese Navy prior to the Second World War. The theory was derived from the writings of American naval historian Alfred Thayer Mahan. In the Decisive Battle Doctrine, the Japanese navy would win a war by fighting and winning a single, decisive naval action. The idea gained broad acceptance following the Russo-Japanese War, where a well-trained, smaller Japanese naval force gained a decisive victory in the Sea of Japan at the Battle of Tsushima, defeating the Imperial Russian Navy of their rival the Russian Empire, a western naval power. Operational plans thereafter were influenced by the effective naval gunnery Japan demonstrated at Tsushima.
From the turn of the century up through the start of the Second World War Japanese planners believed achieving victory in such a battle would be dependent upon the effective use of a strong battleship force. The Japanese triumph at Tsushima led to the naval doctrine of Taikan Kyohō Shugi (), the principle of big ships and gigantic guns. Imperial Japanese Navy planning envisioned assuming a defensive posture and waiting upon the enemy fleet to approach, then destroying it in a sharp battle off the Japanese mainland. Japan's victory over the Imperial Russian Navy validated this doctrine in the eyes of the Imperial Japanese Navy General Staff. Thereafter naval procurement and subsequent deployment of naval assets was based upon the Kantai Kessen doctrine.
Background The Imperial Japanese Navy General Staff was heavily influenced by the writings of the American naval historian Alfred Thayer Mahan. Mahan's writings, including The Influence of Sea Power Upon History, 1660-1783 published in 1890 and The Influence of Sea Power upon the French Revolution and Empire described how British naval power in the Age of Sail had made the British Empire dominant over its rivals and kept it secure. These works were influential in the naval staffs of many nations. Translated into Japanese, they were read at the Imperial Japanese Naval Academy and Naval Staff College. As Britain and Japan were both island nations, the Japanese Navy General Staff felt the British maritime experience was useful and relevant to the future of Japan.
In his writings, Mahan asserts that success in war for the United Kingdom had been dependent upon her control of seaborne commerce. By denying use of the sea lanes to its opponents, Britain had been able to stifle the economies of its enemies, leading to eventual victory. Mahan shows how Britain had made use of a fleet of ships of the line to establish command of the sea. He asserts that the objective of a strong sea power was to build a fleet capable of destroying the enemy's main force in a single battle. By concentrating their ships into a powerful force the British were able to win a decisive victory. Once accomplished, Britain was at liberty to blockade her enemy's ports. Concentration was a key element. Mahan believed that fleet concentration was the most important principle in naval warfare.
In 1896 the Japanese introduced a naval expansion plan. Japan began building battleships, and the four battleships to be built under the plan were to be more powerful in armament and armor than any other warships afloat. This effort to provide the Japanese navy with a qualitative advantage over other naval powers became a hallmark of Japanese planning.
With the onset of World War I, Britain called upon Japan to honor their commitment in the Anglo-Japanese Alliance. Japan did so, joining the Allies. They attacked and took the German colony Tsingtao in China and later performed convoy duties in the Mediterranean. and Pacific eg escorting ANZAC troopships (see Japanese cruiser Ibuki (1907)). At the end of the war Japan gained the German possessions in China, and through the South Seas Mandate Japan gained Pacific islands in Palau, the Marianas, Micronesia and the Marshalls.
Japan's primary goal after World War I was to expand its economic influence and control in East Asia, principally China. In that strategic aim Japan faced opposition from Britain and the Netherlands, who held colonial interests in the region, and from the United States, which sought to protect its territories in Guam and the Philippines, and maintain an economic Open Door Policy in China. In this setting, the naval planners of both Japan and the United States began working out scenarios for how a possible conflict in the Pacific would be fought and won.
The Pacific Ocean, with its vast reaches, was a significant obstacle to overcome. In considering a war in the Pacific against the United States, the Japanese counted on the fact that the size of the Pacific Ocean would in itself be a defense. For the United States Navy to conduct operations against the Japanese, all actions would necessarily be far from their home ports. Travel to the area of combat would consume the fleet's supplies of fuel and food and would limit the amount of time US Navy assets could operate in the western Pacific. Japan could assume a defensive posture and await the US battle fleet. Japanese naval theoreticians, led by Admiral Satō Tetsutarō, argued that a war against the US Navy fought in a single decisive action could be won by Japan.
Japanese naval doctrine traced its origins to Akiyama Saneyuki and Tsushima. The war against Russia culminated in a naval battle in which the outnumbered Japanese fleet prevailed through its superior training and fighting spirit. The Russians had lost 8 battleships and 4,800 dead, while the Japanese suffered the loss of three torpedo boats and 110 dead. It was a decisive victory. This became a template for the Imperial Japanese Navy (IJN). The lesson learned was that future naval confrontations would be decided by the big guns aboard battleships, with the winning side being the side having the larger fleet and the larger guns.
Naval theory
Although major powers such as Great Britain and the United States possessed larger navies than Japan, Japanese planners believed Japan could still win a limited war if its opponents were fighting at a great distance from their home ports in a far-off theater. Naval planners such as Admiral Gonnohyōe Yamamoto estimated that if Japan had a fleet 70% the strength of the United States Navy (USN), then Japan could still fight to a win. To negate the difference in strength, the Japanese hoped to take advantage of the long transit across the ocean to inflict attritional losses of 10 to 20% against the US. The remaining difference was to be made up with the technical superiority of Japanese ships, and with the skill and determination of Japanese sailors. This assumption was built upon two pillars. First, the IJN had to have the weapons and tactics to inflict attritional losses on the US Navy before the decisive battle. Second, Japanese warships needed to possess superior speed and gunnery, capable of hitting at ranges beyond the reach of the US Navy, and had to be manned by very well-trained crews. With this in mind, the IJN spent the entire interwar period preparing for a war against the United States Navy. The IJN developed a strategy of "gradual attrition" to weaken the US fleet prior to its arrival in the western Pacific. Under this plan, Japan would employ submarines, land-based bombers, and light surface forces to whittle down the approaching US fleet to a size that the Japanese could defeat in a fleet-versus-fleet battle. Based on a theoretical US Navy strength of 25 battleships and heavy cruisers split between two oceans, Japan would need a fleet of at least eight first-line battleships. These would be supplemented with eight battlecruisers. Funding for the construction of such a force was passed through the Diet of Japan, in the 8-8 plan. From 1907 to 1920, construction of warships were scheduled with the goal of achieving the 8-8 fleet plan. The battleship program consumed a large percentage of the national budget and moved ahead slowly because of budgetary constraints. In 1920 an IJN building program that would have provided four battleships and four battlecruisers by 1927 was approved by the Diet. These ships were never finished and the 8-8 program never realized, as these plans were superseded by the 1922 Washington Naval Treaty.
The Imperial National Defense Plan in 1907 outlined Japanese naval strategy with the USN as its hypothetical enemy. Prior to any USN advance into the western Pacific, the IJN was to prepare to attack the USN to secure command of the sea. The main battle fleet was to remain in home waters and wait for the approach of the US fleet. It was taken as fact that the time the US fleet could operate in the western Pacific was limited by their need to resupply. This limitation would compel the US commander to commit his force in a single major battle. The nature of this battle was believed certain, and the vision was shared by both the IJN and the USN: the battle would be decided by the big guns aboard battleships. Japanese naval tactics centered on the battle line. Their planners hoped Japan would win such a battle decisively, as they had at Tsushima. The most optimistic prewar Japanese policy envisioned a series of sharp blows followed by a successful major sea battle, which would result in a negotiated compromise with Japan's British and American opponents.
Japanese planning
The Japanese Navy's planning for hostilities against the United States until 1941 was essentially defensive. It depended upon waiting for the approach of the American fleet into the western Pacific. Japan would not carry the war to American shores. The Japanese defensive posture was considerably enhanced after World War I by the South Seas Mandate, in which the League of Nations ceded German possessions in the Pacific to Japan. Japan built bases upon these islands from which Japanese air units could sortie forth to scout and inflict damage upon any approaching fleet. The Japanese counted on these island outposts to wear down the approaching American fleet to a level to near parity where the Japanese Combined Fleet would meet them.
Until the 1920s, the Japanese expected this decisive battle to occur near the Ryukyu Islands just south of Japan and to be conducted by surface forces. However, as technology advanced, the projected location was moved farther eastward. From the mid 1920s to 1940, the line was somewhere between the Bonin Islands (some 540 nautical miles south of Tokyo) and the Mariana Islands.
According to the first stage of the battle plan, fleet submarines would first be used to weaken the American fleet by 10%, then bombers from land bases and aircraft carriers would inflict another 10% casualties. Air strikes launched from carriers would neutralize the American carrier fleet. Fast heavy cruisers working with destroyer flotillas would attack the US battleships at night, making use of their long-range Type 93 torpedoes to inflict further losses. Now facing a depleted enemy at the limit of his supply chain, this would be the "decisive" stage of the battle, when the battleships of the Combined Fleet, centered on the modern Yamato class, would engage the US battle line. Finally, the older battleships would destroy the surviving remnants of the American fleet.
Advances in carrier aircraft and carrier doctrine
In about 1932–33, the IJN began to shift the targets of its air forces from the enemy's battleships to their carriers. By mid-decade, with the improved performance of bombing aircraft, particularly the dive-bomber, the destruction of the enemy's carrier force became the focus of Japan's carrier forces. The emerging concept of mass aerial attack shifted carrier air power away from the defense of the main battle force to attack on targets over the horizon. The IJN's air war in China brought home to nearly its entire leadership the tremendous offensive potential of aerial weapons.