What if Germany had never declared war on the United States during World War II?
Scholars and analysts have long wondered whether this represented one of the great “what-ifs” of World War II; could the Germans have kept the United States out of the war, or at least undercut popular support for fighting in the European Theater, by declining to join the Japanese offensive?
Was the decision to declare war on the United States, effectively relieving the Roosevelt administration of the responsibility of mobilizing American sentiment for war in Europe, among Hitler’s greatest blunders?
Probably not. Washington and Berlin agreed that war was inevitable; the only question was who would fire the first shots.
The United States and Germany were at war in all but name well before December 1941. Since early 1941 (at least) the United States had shipped war material and economic goods to the United Kingdom, enabling the British government to carry on with the war. American soldiers, sailors, and airmen served in the British armed forces, albeit not in great numbers. And in the late summer of 1941, the United States effectively found itself at war in the Battle of the Atlantic. The Greer Incident, in which a U.S. destroyer tangled with a German U-boat, served to bring the conflict into sharp focus.
The Fireside Chat delivered by President Roosevelt on September 11, 1941 made clear that the United States was already virtually at war with Germany:
“Upon our naval and air patrol -- now operating in large number over a vast expanse of the Atlantic Ocean -- falls the duty of maintaining the American policy of freedom of the seas -- now. That means, very simply, very clearly, that our patrolling vessels and planes will protect all merchant ships -- not only American ships but ships of any flag -- engaged in commerce in our defensive waters. They will protect them from submarines; they will protect them from surface raiders.
It is no act of war on our part when we decide to protect the seas that are vital to American defense. The aggression is not ours. Ours is solely defense.
But let this warning be clear. From now on, if German or Italian vessels of war enter the waters, the protection of which is necessary for American defense, they do so at their own peril.”
This declaration did not simply apply to U.S. territorial waters. The United States would escort convoys filled with military equipment to Europe with surface ships and anti-submarine craft, firing at will against any German submarines, ships or planes that they encountered.
Moreover, even U.S. ground forces had begun to participate in the war. In early July 1941, the U.S. Army and U.S. Marine Corps, with Navy support, began deploying to Iceland. The Americans relieved British and Canadian troops who had invaded the island a year earlier.
In the long run, Hitler (and the rest of the German government) believed that confrontation with the United States was virtually inevitable. The U.S. had intervened in 1917 on behalf of Russia, France, and the United Kingdom; it was almost certain to do so again. U.S. behavior in 1941 reaffirmed this belief. Starting the war on German terms, before the U.S. was prepared to effectively defend itself, was the consensus position within the German political and military elite.
And so Germany declared war on the United States not out of a fit of pique, but rather because it believed that the United States was already effectively a belligerent, and that wider operations against the U.S. would help win the war. In particular, the Axis declaration of war enabled an operation that the Germans believed was key to driving Britain out of the conflict; a concerted submarine attack against U.S. commercial shipping. Although the Kriegsmarine had targeted U.S. vessels in the months and years before Pearl Harbor, it radically stepped up operations in the first months of 1942, launching a major effort just off the U.S. Atlantic seaboard.
The German tactics were devastatingly effective against a U.S. military that lacked good tactics, equipment, and procedures for fighting the U-boats. For their part, British military and political authorities worried that the German offensive might work, destroying enough shipping to cut Britain’s lifeline to North America. The Royal Navy and Royal Air Force quickly dispatched advisors to the United States in an effort to staunch the bleeding, but 1942 nevertheless proved the most devastating year of the war for shipping losses. Overall, Operation Drumbeat proved far more successful for the Axis than the Japanese attack on Pearl Harbor.
But What If…
If, despite all this, Germany and Italy had somehow managed to avoid an open declaration of war against the United States, conflict would have continued in the North Atlantic. The U.S. would have continued to supply Britain and the Soviet Union with war material, potentially with somewhat more secure lines of supply, especially if the Germans continued to avoid attacks along the Atlantic seaboard.