This post first appeared on Today in Alternate History with input from Allen W. McDonnell, Robbie A. Taylor, Eric Oppen, and Thomas Wm. Hamilton.
April 18, 1942 -
Admiral Yamamoto feared that the surprise attack on Pearl Harbor would "awaken a sleeping giant". But due to a twist of fate, the consequences would prove to be far worse as the Soviet Union, British Empire, and Free China combined forces with the United States, assisting the Americans in seeking to wreak their revenge.
Japan had established the puppet state of Mengjiang, which bordered the Soviets, while the two countries were not at war. Stalin had major problems in the west from the German invasion and was heavily dependent on supplies coming in to the Far East via Vladivostok. Consequently, it was only a wild card factor that gained Soviet support for Lt-Col James Doolittle's Tokyo Raid. A significant ship from the Soviet Pacific fleet had been on a port call to Pearl Harbor, where it was destroyed in the Japanese attack. This was a terrible mistake since the Japanese had been soundly defeated by the Soviets in a Border War, prior to a 1939 ceasefire. Unafraid of Japanese reprisals, Stalin secretly gave his approval for the US Navy aircraft carrier USS Hornet to deliver a substantial force of B-25B Mitchell medium bombers to Vladivostok.
Without this logistical assistance, Doolittle would have had to have led a smaller force launching at sea from the Hornet itself. Instead, the Raid by a much larger force created a reciprocal amount of significant damage at the very top end of President Roosevelt's expectations. The impact on the Japanese high command was hugely disproportional. The fact that the bombers arrived unexpectedly and unopposed was another brick kicked from the foundations of their outpost perimeter defense.
Moreover, there were wider consequences that Chiang Kai-shek partly foresaw - after all, he was most familiar having fought the Japanese Empire the longest. He correctly anticipated a realignment of naval forces with most analysts suggesting the northern Pacific and even into the Bering Sea to cut off supply routes to Russia. But, to protect the Home Islands, instead the Japanese set about punishing the United States with further revenge attacks on America's west coast.
Americans were deeply worried about the "still very badly undermanned west coast" and Chief of Staff George Marshall discussed a "possible attack by the Japanese upon our plants in San Diego and then a flight by those Japs down into Mexico after they have made their attack." Marshall's visit would foreshadow the San Diego Raid, a second Pearl Harbor-style attack which would bring the Second World War to American shores. The costs to Japan were far greater than the momentary political benefits being that America was fully on a war footing and with radar tracking in San Diego spotting the raid.
Author's Note:
In reality, the Bombers were launched from the USS Hornet, and Johnson speculated from China where the crews landed. Eight US aviators were captured by Japanese forces, and three of these were later executed. All but one of the B-25s were destroyed in crashes, while the 16th landed at Vladivostok.
The consequences of the Doolittle Raid were most severely felt in China, where Japanese reprisals caused the deaths of 250,000 civilians and 70,000 soldiers. Nevertheless, Chiang Kai-shek awarded the raiders China's highest military decorations, and predicted (in his diary) that Japan would alter its goals and strategy as a result of the disgrace. Indeed, the raid was a shock to the staff at Japanese Imperial General Headquarters. As a direct consequence, Japan attacked territories in China to prevent similar shuttle bombing runs.