September 27, 1941. A plain, ugly cargo ship called the SS Patrick Henry slides down the ways into the water, and almost nobody watching quite realizes they are looking at a war-winning weapon. She is the first of the Liberty ships, and before the war is over, American yards will build more than two thousand seven hundred of them, an avalanche of steel that will bury the U-boats under sheer numbers. The problem the Liberty ship solved was brutal arithmetic. Britain, and later the whole Allied war effort, floated across the ocean on merchant shipping, and German U-boats were sinking that shipping faster than it could be replaced. If the Allies could not build cargo ships faster than the submarines could sink them, Britain would be starved out and no invasion of Europe would ever be possible. It was, at bottom, a production race, and in 1941 the Allies were losing it. The American answer was to stop thinking like traditional shipbuilders and start thinking like automakers. The Liberty ship was a deliberately simple, standardized design, nothing elegant, just a rugged, no-frills freighter that could be mass-produced. And crucially, the ships were welded rather than riveted, and built from large prefabricated sections made all over the country and then assembled at the yards. This let unskilled and semi-skilled workers, many of them women, the real "Rosie the Riveters," turn them out at a speed that had never been seen before. The SS Patrick Henry, named for the American revolutionary who cried "give me liberty or give me death," which is where the ships got their name, launched on this day as the first of them. Then the numbers went berserk. As the yards, above all Henry Kaiser's, mastered the process, the time to build a Liberty ship fell from months to weeks to days. In one famous stunt, a yard assembled a complete Liberty ship in under five days to show it could be done. On average, by the peak, American yards were launching about three of these ships every single day. More than twenty-seven hundred were built in total. It was one of the greatest feats of industrial production in human history. And it won the Battle of the Atlantic as surely as any warship or aircraft. The U-boats kept sinking ships, but they could no longer sink them faster than America could build them, and eventually the escort carriers and the long-range aircraft and the code-breakers turned and slaughtered the submarines themselves. The tonnage the Liberty ships carried, the tanks and trucks and food and fuel and troops, was the physical stuff of Allied victory, the flood of material that let Britain hold on, that supplied the Soviet Union, that put the armies ashore in Africa, Italy, and finally Normandy. The Patrick Henry that launched on the 27th was homely and slow and built to a pattern, but she and her twenty-seven hundred sisters were a weapon Hitler had no answer for, the industrial might of the United States turned into a bridge of ships across the Atlantic. Sometimes wars are won not by the most brilliant weapon but by the one you can build faster than the enemy can destroy it, and that story began with this plain ship sliding into the water on this day.