The Battle of the Atlantic took a sharp turn toward Axis power when Operation Rheinubung became one of the German navy's most glorious successes. At the head the squadron was the seemingly invincible Bismarck, the largest battleship in history up to that time. Like its namesake, Otto von Bismarck (1815-1898), the “blood and iron” of the German people would overwhelm Britannia's rule of the waves and establish a period of German domination, cutting off supplies desperately needed by the British war effort.
The British, meanwhile, worked to limit the growth of German naval power. In addition to forcing them to divert resources to the land army, they destroyed the remnants of the French navy held by Vichy France in Operation Catapult on July 3, 1940. The British approached the French fleet at Mers-el-Kébir in Algeria and opened fire after an ultimatum asking for any ships to join the Free French Navy rather than falling into the hands of the Germans. While many French ships throughout the Mediterranean and world did just that, the British felt themselves forced to destroy the fleet to keep it out of Hitler's hands. In a surprise attack, the British sank the battleship Bretagne, damaged six other ships, and killed nearly 1,300 French sailors.
Attack at Mers-el-Kébir drove a rift between Churchill and the French Resistance under General Charles de Gaulle, but the British considered the risk of angering an ally reasonable compared to an Atlantic full of German ships. Hitler recognized the British fear of losing the naval superiority they had held for nearly two centuries and decided to redouble his efforts on Plan Z. Initially, he had only planned to neutralize the French fleet; now he decided to rebuild it into a Mediterranean battlegroup to aid his Italian allies. While resources were strapped as the war began with Russia, he decided Germany would make the best use of what it had. Ships would act in orchestrated battle groups where heavy escort would overwhelm any British resistance.
On May 18, 1941, Operation Rheinubung (“Rhine Exercise”) began, forming up the impressive German fleet in the Baltic and storming the Denmark Strait on May 24 to break the British blockade. While only the Bismarck and heavy cruiser Prinz Eugen might have been ready for the battle, Hitler pressed his navy to finish repairs on the Gneisenau and Scharnhorst battleships and even rush to complete the sea trials for the Tirpitz, Bismarck's sister ship. Aided by U-boats as skirmishers and (whose arm had been wrenched by Hitler into cooperation), the sortie into the Atlantic began with the devastating battle off Norway where the Bismarck sank the HMS Hood, the pride of the Royal Navy. Britain reeled, and Churchill famously demanded, “Sink the Bismarck!” The Navy swarmed to attack the battle group, focusing specifically on the flagship, but the German iron seemed unbreakable. After several more devastating assaults, the German ships finally turned back to France, where they would refuel and turn out into the Atlantic again to prey on Allied commercial shipping.
Also on May 24, FDR gave his speech announcing “unlimited national emergency” as Germans had seemingly come to gain the advantage in the Battle of Atlantic. Rather than repeating his 1933 idea of “the only thing we have to fear is fear itself”, he addressed America with a dire warning of what Nazi takeover of the West would mean: restrictions on worship, workers enslaved to a foreign military machine, and children stolen into the ranks of the Hitler Youth. He emphasized his Pan-American Security Zone (which reached nearly to Iceland) and stated that German naval attack within the zone would be paramount to a declaration of war. Hitler, on May 27, announced German control of the seas.
When Germany began raids on the Canadian coast in September of 1941, Congress voted for a declaration of war, and the United States formally joined the Allies. The action quickly brought the East Coast Battles, where German battleships and newly refitted French aircraft carriers launched bombing raids on Boston, New York, and Washington, D.C. Britain nearly folded as civilians suffered starvation and almost free attack from German planes, but finally the tide of the war turned against Germany in 1943 when the Bismarck was damaged beyond repair and scuttled in the Battle of Nassau. Taking up courage to counterattack, the Allies coordinated invasions, finally breaking the German resistance with the atomic bombs of 1946.
In reality, the Royal Navy sank the Bismarck. Hitler took little notice of the French fleet, considering it out of the way and focusing on his land and air forces. After sinking the Hood, the Bismarck was ruthlessly pursued by the Royal Navy until two carriers, three battleships, four cruisers, and seven destroyers converged to destroy the Bismarck utterly, with 2,200 sailors drowning along with her.