Was Pearl Harbor really a surprise attack?

The short answer

• The oil clock ran out. The August freeze described in Chapter 10 made oil stocks a measure of time as well as supply. Japanese planners expected their capacity for war to decline as those stocks fell. On 6 September the Imperial Conference set a sequence: negotiate until October, then decide on war. Konoe sought a summit, but Washington wanted prior concessions on China. His government fell, and Tōjō inherited the timetable. Hull’s note on 26 November marked a decisive diplomatic breakdown, yet the fleet had sailed that morning. The calculation about fuel had already put the operation in motion.
• Yamamoto’s wager against his own judgment. Yamamoto knew the United States from Harvard and service as naval attaché in Washington. He opposed war with it, telling Konoe that he could “run wild for six months or a year,” but had no confidence thereafter. His Pearl Harbor plan began with a conditional judgment: if Japan went to war, the American battle fleet must be prevented from disrupting the southern offensive. A spectacular blow might also discourage a long American struggle. The first aim gave the attack an immediate military purpose; the second required a political response that Yamamoto himself had reason to doubt. His warning left the problem of what Japan could accomplish after the first months.
• Washington expected war — somewhere else. On 27 November American warnings went to Pacific commands. Officials had read Japanese diplomatic communications through MAGIC and expected war, with the Philippines or Malaya considered likely targets. Hawaii seemed distant, its water too shallow for torpedoes, and such an attack too audacious. Tokyo had studied Taranto (Ch. 11) more carefully. Oahu’s radar detected the incoming formation 132 miles away. The duty officer believed it was a flight of B-17s expected from California. The instrument supplied a contact; the explanation given to it prevented that contact from becoming an effective warning.
• Hitler chose the world war. The Tripartite Pact required assistance to Japan if it were attacked. Japan had attacked the United States, so Germany had no treaty obligation to declare war. Hitler chose to do so on 11 December. His Reichstag speech and table talk suggest his reasoning: U-boats were already fighting American convoy escorts in an undeclared naval war, and Japan might occupy the United States in the Pacific for years. His racial contempt for a “mongrel” nation also led him to underestimate American capacity. His decision joined the wars represented on the atlas’s separate maps.

What it changed

The perimeter, then the tide. Japan’s advance continued for roughly the six months Yamamoto had described. Malaya, Singapore in February 1942, the Indies and the Philippines fell; Singapore was a particularly severe imperial capitulation. Then the Battle of the Coral Sea checked an advance in May. At Midway in June, American carriers absent from Pearl Harbor helped sink four of the six Japanese carriers that had attacked it. The WW2 atlas takes up the war that this atlas ends by beginning.

The arsenal opens both doors. Roosevelt could pursue “Europe first” more easily with public support after Germany’s declaration. Lend-Lease was already supplying Britain and the USSR, and became a means of sustaining the global coalition. By war’s end the program had provided about $50 billion in matériel, including Studebaker trucks used by the Soviet Union and food shipped to Britain.

Asia’s empires never come back. The tan across the southern half of the map represents empires whose authority Japan’s victories shook. An Asian power had defeated European colonial forces in weeks. After 1945 European governments attempted to restore their rule, but India became independent in 1947 and Indonesia in 1949; Indochina followed after wars covered in the Cold War atlas. Japan’s conquest was defeated, yet the imperial world it attacked did not survive unchanged.