From early 1941 onward, the Japanese were establishing and refining their war strategy which, as regards the U.S., which translated into a three part movement: attacking the Pacific Fleet in Pearl Harbor, establishing a defensive line across the Central Pacific, and attriting the U.S. fleet when they moved westward. Meanwhile, the United States did not want war with Japan and yet ended up in exactly the war Japan did not want: an extended war of attrition and logistics pitted against the manufacturing power of American industry and resources.

The historical record is quite clear that the Roosevelt administration was committed to a “Germany-first” strategy, stopping Hitler in Europe. Hitler’s facism was viewed as the modern plague that must be stopped lest it infect the whole world. In 1941 the U.S. was  engaged in an undeclared shooting war with Nazi submarines in the North Atlantic that was a precursor to what awaited the U.S. in the event of a declared war. In the first half of 1942, almost 600 allied merchant ships were lost to German U-boats. The Roosevelt Administration needed to keep Britain in the war with supplies and a key to that was avoiding war with Germany. The last thing Roosevelt wanted was a war in the Pacific. 

Jonathan Utley observes “No one during the fall of 1941 wanted war with Japan. The Navy preferred to concentrate on the Atlantic. The Army said it needed a few more months before it would be ready in the Philippines. Hull had made the search for peace his primary concern for months. Roosevelt could see nothing to be gained by a war with Japan. Hawks such as Acheson, Ickes, and Morgenthau argued that their strong policies would avoid war, not provoke one.”

The administration maintained military sales to China with the goal of keeping the Soviets in the fight, focused on Germany without having to worry about an eastern front attack by Japan. With military supplies delivered via the “Burma Road” the Chinese were able to continue to keep IJA troops engaged, bogged down, and thus Japan was unable to initiate any incursions into Siberia or Mongolia. This ensured that the Soviets did not have to wage a two-front war. 

But there was a limit: the U.S. administration was not willing to go to war with Japan over China. With Japan controlling all significant Chinese ports, the only two available supply routes were the Burma Road and smuggling via Hong Kong. The U.S. goal was to provide enough arms to China so as to deter or inhibit a Japanese advance into Southeast Asia.  This goal was advanced by relocating the Pacific Fleet to Pearl Harbor from their California ports, the imposition of economic sanctions, and beginning a slow build up on forces and long-range bombers in the Philippines. The administration was mistaken in their belief. The U.S. presumed realism and rationality on the part of the Japanese and failed to understand that severe sanction (i.e. the financial freeze and de facto oil embargo) would be tantamount to an act of war.

The Germany First Priority

The U.S. posture vis-a-vis Japan was complicated by a “Germany First” outlook that guided U.S. policy even before Pearl Harbor and shaped military planning and diplomacy. President Roosevelt and military planners believed that Nazi Germany posed the greatest global threat. In November 1940, Chief of Naval Operations Adm. Harold Stark recommended a defensive posture in the Pacific as regards Japan while prioritizing the defeat of Germany and Italy in Europe. He produced this recommendation in a memorandum that came to be known as “Plan Dog” which laid out U.S. options in the event of war against Germany, Japan, or both. He reviewed several possible scenarios and plans, lettering them from “A” through “D,” and ultimately recommended Plan “D.” At that time, the U.S. Navy’s phonetic alphabet for “D” was “dog”: hence the name.

U.S. leaders came to realize that the scenarios underlying the older “color-coded” war plans were based on the assumption that the United States would fight a war against a single enemy one-on-one. It was increasingly clear that these were no longer realistic assumptions. The United States was increasingly likely to face war against multiple enemies across the globe. In which case, the country would need allies, which meant Britain, Australia, New Zealand, and the Netherlands, all of whom had interests in the Southwest Pacific. 

By November 1940, France had fallen, and Britain stood alone against Nazi Germany and its Italian allies. The German bombing campaign against Britain had begun. Recognizing the consequences of a British defeat, President Franklin Roosevelt had been gradually increasing U.S. support to the United Kingdom, first through the “cash and carry” policy in September 1939, and then through the “destroyers for bases” deal in September 1940  which became the December 1940 Lend-Lease program. In Asia, meanwhile, Japan’s invasion of China continued, and in September they occupied the northern part of French Indo-China. 

Roosevelt was constrained by public opinion, which strongly opposed U.S. involvement in another major foreign war. Stark’s memorandum, therefore, came at a critical time—before the United States was formally at war, but as war was looking more and more likely. It was by no means clear what course the United States should or would follow. Admiral Stark laid out the essence of the grand strategic problem facing the United States, and he concisely crafted the best courses of action. Plan A was war with Japan only and no allies. Plan B was war with Japan only supported by British Allies. Plan C was war with the Axis allies and no allies of our own. Plan E was no stay out of the wars all together

Plan Dog was we’d be at war with Germany and Italy in support of Britain while Japan was not yet involved. Any involvement with Japan would be at the initiation of the United States.

“…our major national objectives in the immediate future might be stated as preservation of the territorial, economic, and ideological integrity of the United States, plus that of the remainder of the Western hemisphere; the prevention of the disruption of the British Empire… and the diminution of the offensive military power of Japan, with a view to the retention of our economic and political interest in the Far East. It is doubtful however that it would be in our interest to reduce Japan to the status of an inferior military and economic power. A balance of power in the Far East is as much to our interest as a balance of power in Europe.” (emphasis added)

Admiral Stark was not optimistic of Britain’s ability to remain in the war and as a result he recommended an immediate, intentional build up of U.S. Army and Navy capability. He wrote, “Until such time as the United States should decide to engage its full forces in war, I recommend that we pursue a course that will most rapidly increase the military strength of both the Army and the Navy, that is to say, adopt Alternative (A) without hostilities.”

President Roosevelt took Stark’s recommendations regarding the build up of the nation’s military capability, but President Roosevelt soon concluded that Nazi Germany posed the greatest global threat. The Plan Dog memorandum recommended that if the United States were forced into war against both Germany and Japan, it should fight defensively in the Pacific while concentrating resources on defeating Germany in Europe. As a result U.S. rearmament focused heavily on the Atlantic theater, increasing support was given to Britain through Lend-Lease, and the Navy was deeply engaged in convoy protection in the Atlantic and already clashing with German submarines.

Because Roosevelt wanted to prevent Japan from expanding while the U.S. focused on Europe, Washington set out to deter Japanese expansion through economic pressure rather than immediate war. Japanese diplomats and naval intelligence closely followed these developments. Tokyo concluded that the United States expected eventual war with Germany, were prioritizing European commitments and so the U.S. resources would be divided between two oceans. From the Japanese perspective, this created a temporary window of opportunity in the Pacific.

The “Germany First” strategy shaped Japanese thinking in two ways. First, it suggested that the United States might avoid a prolonged Pacific war if forced to fight Germany simultaneously. Second, Japanese planners believed that if the Pacific Fleet were crippled, the United States would be strategically compelled to concentrate on the European war. This assumption encouraged the idea that a surprise strike could secure time for Japan to seize Southeast Asian resources, establish a defensive perimeter in the Central Pacific, and force the United States to negotiate their exit from the Asia-Pacific conflict

The unintended consequence of all this was “Plan X” – not envisioned by Admiral Stark: war with the Axis allies, a two-ocean war, all initiated by Japan’s attack on Pearl Harbor.  Japan’s reasoning underestimated American political and military capacity. Instead of forcing strategic restraint, the attack on Pearl Harbor produced immediate ramp-up in U.S. mobilization and a long-term industrial expansion that Japan could never hope to match.

Image credit: various photographs from Naval Aviation Museum, National World War II Museum, and US Navy Archive | Plan Dog available online at the FDR Library at Marist College.

While the Imperial Japanese Army (IJA) lurched into escalation through a series of “incidents” in China and suffered defeat at Nomanhan at the hands of the Soviets, the Imperial Japanese Navy (IJN) followed a very different strategic logic. It was one that was more calculated and globally oriented, though ultimately no less expansionist.

Both Japan and the U.S. were adherents of the theories of Alfred Thayer Mahan (1890) who posited that national greatness is inextricably linked to sea power, defined as the ability to control vital maritime trade routes and project naval force. Mahan argued that a large, concentrated, offensive, steam-driven navy (as opposed to sail) supported by merchant shipping and overseas colonies, is essential for securing economic wealth and international influence.

By the early 1930s, the IJN had concluded that Japan’s survival depended on maritime access to resources. As such, it was clear that the decisive threat was the United States, not China or the Soviets (IJA’s concerns). IJN leaders, many of whom had served or studied in the United States, knew war, if it came, would be long, decided by naval forces, and dependent on control of the seas. This contrasted sharply with the Army’s fixation on continental expansion, border clashes and the ideological fixation against communism.

Decisive Battle Doctrine

The Navy’s planning revolved around kantai kessen (decisive fleet battle) which is described in a previous post: War Plan Orange. In short, the operational concept was to allow the U.S. Pacific Fleet to steam west 3,000 miles to the Western Pacific (Mahan’s theory was that for every 1,000 miles of ocean transit a fleet would lose 10% of its combatant strength). But along the way to attrit the U.S. Fleet with submarines and air attacks. The now weakened U.S. Fleet would be destroyed in a decisive surface battle in Japanese waters.

This doctrine was at the root of naval construction efforts: battleships, cruisers, destroyers, and aircraft carriers. The IJN was at the forefront of aviation, not only for deployment on carriers, but also for island-based airfields across Micronesia (Truk, Saipan, Palau and others). Such installations were sited on expected lines of advance of the US Fleet and served as “unsinkable aircraft carriers.” In this same vein, Japan emphasized long-range naval aviation, knowing that would be a key to success in the open waters of the Pacific. The Japanese also greatly expanded their submarine fleet.

The IJN and China 

When the Army expanded the Sino-Japanese war after the Marco Polo Bridge Incident, the Navy viewed it as a dangerous distraction from the larger strategic threat. Nonetheless, the Navy took on the natural role of blockading the Chinese coast, seizing key ports (Shanghai, Canton), and protecting maritime supply lines for Army forces. At the same time, the IJN took the opportunity to develop experience in long-range bombing by extensive naval air bombing of Chinese cities. The Navy hoped the whole “China affair” would quickly move to a political settlement so that resources and attention would focus on the coming naval battles

Internal Navy Debate: Treaty Faction vs. Fleet Faction

The Washington Naval Treaties of 1922 divided the IJN for the next 20 years. The resulting factions still mattered right up to 1941. In short, the Treaty Faction favored naval arms limitation, feared war with the U.S. and preferred diplomacy and gradual expansion. The Fleet Faction rejected treaty limits as shameful and dishonorable, sSought parity through qualitative superiority, and held that war with the U.S. was inevitable. By the late 1930s, the Fleet Faction dominated, especially after Japan withdrew from naval treaties in 1934 and began to build new combatants exceeding the limitation of the treaty. A key concept of the Fleet Faction was parity with the United States. While they knew the U.S. could outbuild Japan, they also knew that the U.S. was required to be a two-ocean navy. The Fleet Faction did not have many officers who were familiar with the U.S. industrial capacity or resources. Their basic assumption of parity in the Pacific was seriously wrong, and in addition, the focus on combatants severely diminished the production of merchant shipping and especially fleet oil tankers. In 1939, despite having a large merchant marine, Japan still relied on foreign-flagged vessels for nearly 30% to 40% of its shipping needs to sustain its economy, particularly for raw materials and oil. This persisted even into 1941. Japan’s military and industrial goals meant that it had to import 94% of requirements for oil, aviation fuel, gasoline, lubricants, and general purpose oil-based products.

Japan’s reliance on pre-war, Allied-flagged tankers, which ceased upon war declaration, left them with a massive logistical gap. Japan did not possess enough specialized oil tankers to adequately transport oil from Southeast Asia (the “Southern Resource Area”) to Japan after Pearl Harbor. In 1941 Japan required 32 million barrels of oil annually. This equated to 5 million (dead-weight) tons of shipping. Japan’s tanker fleet was inadequate, with only 49 merchant tankers (approx. 587,000 tons) available at the start of the war – only 10 percent of their needs. The lack of tankers was a critical failure in planning, as Japan failed to prioritize building enough tankers to secure their oil lifeline. While they quickly conquered oil fields, allied submarines and aircraft sank tankers faster than they could be replaced, severely crippling the oil supply line. 

IJN Operational Planning

The Army’s 1939 defeat by the Soviets at Nomonhan had an impactful, yet indirect effect on naval policy. The IJN concluded that continental expansion (China, Siberia, Mongolia, etc) was a strategic dead end. As such Japan must look south, not north. This reinforced the Navy’s preferred Southern Advance (Nanshin-ron) to Southeast Asia, the Dutch East Indies, and British Malaya

From the autumn of 1939 forward, naval war plans increasingly assumed U.S. embargoes and thus the need for preemptive action. Even then IJN leaders repeatedly warned the Diet and the Emperor about U.S. industrial superiority, repeatedly stressing that a long war with the United States could not be won. Oil reserves sufficient for roughly 18–24 months; after that, the fleet would be immobilized and any war fought later would be unwinnable.

No one expressed this more bluntly than Admiral Yamamoto, the architect of the Pearl Harbor attack, who warned that Japan could: “Run wild for six months… but I have no confidence after that.” It was sober professional judgment shared widely in naval circles.

The IJN lived with a deep internal contradiction. It understood with remarkable clarity that Japan could not win a long war against the United States, yet it simultaneously embraced plans that assumed a short, decisive victory would somehow occur. This was not simple irrationality. It was a coexistence of strategic realism and catastrophic optimism, reinforced by culture, doctrine, and institutional pressure.

Knowing a long war was unwinnable, it was clear that realism led not to peace, but to a compressed decision space. Diplomacy required abandoning China which was politically impossible. Waiting meant fuel exhaustion which was strategically fatal. Therefore, war now was preferable to war later. This logic did not say Japan could win a long war. It said Japan must force a short one.

The planning for the Attack on Pearl Harbor captures the paradox perfectly. The plan was realistic: neutralize the U.S. Pacific Fleet early. buy time to seize oil-rich territories, and establish a defensive perimeter too costly to break. The plan was catastrophically optimistic because it hoped the Americans would lose the will to fight, the U.S. would seek to negotiate after early setbacks, and so Japan could dictate terms before U.S. industrial power fully mobilized. Naval planners did not believe Japan could outbuild the U.S. They believed it could outshock it.

War Games

In the years before 1941, the IJN prided itself on war gaming as a mark of scientific modernity. They were conducted at the Naval War College; using detailed maps, counters, and probability tables; and overseen by highly trained staff officers. These war games were treated as tools for refining doctrine, proof of intellectual seriousness, and reinforcement of professional military identity. But they were not neutral experiments. They were embedded in the doctrine of decisive battle thinking.

Nearly all IJN war games began with non-negotiable assumptions: war would be decided by a single climactic encounter, the U.S. forces would advance methodically across the Pacific, and Japan would attrit the enemy and then strike decisively. Because these assumptions were never questioned, war games tested how to win the decisive battle not whether the strategy itself made sense. This meant strategic failure was excluded by design, including one of the most important assumptions: attrition. 

To give you an idea, IJN war games consistently assumed elite pilots survived at implausible rates, ignored replacement shortfalls, underplayed maintenance and fatigue and treated fuel and logistics as abstract variables. Attrition was systematically minimized.  Why? Because acknowledging attrition meant acknowledging time and time favored the United States. Thus, war games preserved optimism by compressing time out of the model.

The War Games always modeled the success of the decisive battle. It never modeled the war of attrition in which they were engaged.

The Fatal Flaw

What realism failed to penetrate was American political culture. While IJN leaders understood U.S. industry. They underestimated the U.S. public reaction of rage, the resulting unity, and capacity to “turn on a dime” to a war economy.  Japan achieved the shock it sought but not the reaction. Instead of weakened resolve, Pearl Harbor produced total mobilization, political unity, and a war effort that erased Japan’s initial advantages within a year. By December 1942, a year after Pearl Harbor, the U.S. was on the offensive having achieved a decisive result at the Battle of Midway, was close to driving the IJA from Guadalcanal, and was turning back the Japanese in New Guinea. Meanwhile, the shipyards and factories were producing ships, planes and pilots at rates that would soon overwhelm the Japanese. At the same time the Japanese merchant fleet was being methodically reduced by unrestricted submarine warfare.

Image credit: various photographs from Naval Aviation Museum, National World War II Museum, and US Navy Archive.

When discussing the rise of militarism in Japan’s Meiji Era, it was mentioned in passing that Japan adopted a British model for its Navy and a Prussian model for its Army. Japan’s preference for Prussian/German military models was not accidental or sudden. It grew directly out of choices, experiences, and disappointments made during the late Tokugawa and early Meiji years. 

By the late Tokugawa Shogunate period there were groups that were imperial loyalists and wanted to end the rule of the shoguns and reform the nation under the Emperor. The tensions ultimately lead to the Boshin War (1868–1869)  which pitted the imperial loyalists (primarily the Satsuma, Choshu, and Tosa domains) against the Tokugawa shogunate and its allied northern domains. The Shogunate forces had taken on French military methods, tactics, and weapons. They failed to save the Tokugawa Shogunat.

The victorious imperial loyalists who formed the Meiji Era drew lessons from their opponent’s defeat: (1) military reform could not be separated from political legitimacy and national unity, (2) the shogun supporters had adopted methods tied to a fallen regime (losers in the Franco-Prussian War). This stigma mattered enormously in Meiji political culture.

What Japan saw in Prussia was a small-to-mid-sized state defeating a great power with victory through universal conscription, a professional general staff, transportation and mobilization planning, and tight civil–military integration. To Meiji leaders, Prussia looked like Japan: late-developing, resource-conscious, and surrounded by potential enemies. Of supreme importance was that Japan needed a land army first, to suppress internal revolts and deter Russia and China.

Prussia offered something France and Britain did not: a theory of the army’s constitutional role. The key ideas were that the army serves the state (in this case, the Emperor); the officer corps embodies loyalty, discipline, and moral authority; and civilian politicians do not micromanage military doctrine. These principles aligned seamlessly with Emperor-centered legitimacy, fear of partisan politics, and the desire to prevent another “shogunate.” The Army would be a servant to the Emperor and therefore the State. Japan did not simply copy Prussia. It chose Prussia because Prussia solved Japan’s Meiji-era problems.

The Meiji Constitution encoded Prussian assumptions with the army and navy answering directly to the Emperor; military ministers required active-duty officers, and the Diet (Parliament) had limited control over defense policy. This arrangement prevented party politics from controlling the military and reflected Prussian constitutional monarchy rather than British parliamentary supremacy.

In the short term, Japan rapidly created  a modern, disciplined army that experienced success in the Sino-Japanese War (1894–95) and Russo-Japanese War (1904–05). But along with that success came an environment where the seeds of later insubordination and factionalism were sown. 

• The military had weak civilian oversight (the military occupied 4 seats in the cabinet and held a virtual veto over any decisions by civil government), 
• Military autonomy was institutionalized by the failure/inability of the civil government to control military operations or hold military leadership responsible (examples include the Mukden Incident in 1931, the Marco Polo Bridge incident in 1937 and the Nomanhan Incident in 1939). The Marco Polo incident was the action that began the 2nd Sino-Japanese War which was the start of the larger Asia-Pacific War, and 
• Radical factions within the military had little qualms about assassinating civil leaders, including the Prime Minister, that they felt were obstructing their aims.

Ironically, the very features that appealed to the first generation of Meiji leaders were the root causes that destabilized civilian government in the 1930s and contributed to the start of the Asia-Pacific War.

Image credit: various photographs from Naval Aviation Museum, National World War II Museum, and US Navy Archive.