U-boat
Germany's submarine, which nearly starved Britain into surrender in 1917 and, by sinking ships without warning, dragged America into World War I.
The German word is Unterseeboot, undersea boat, shortened to U-boot and anglicized to U-boat. The machine was crude by later standards: a cramped steel tube that ran on diesel engines at the surface and battery power beneath, able to stay down only a few hours before it had to rise and breathe. Yet in four years of war this awkward device came closer to defeating Britain than the entire German battle fleet, and in doing so it helped destroy the country that built it.
The logic and the flaw
Britain was an island that could not feed itself. It imported much of its food and most of the raw material for its war industry, all of it carried by merchant ships. Germany, penned in by the Royal Navy's surface blockade, could not challenge those ships in open battle. So it went under them. The strategy was simple arithmetic: sink the merchantmen faster than Britain could replace them, and the island would have to sue for peace.
The flaw was written into the weapon. A submarine's one real advantage is that it cannot be seen, and a hidden ship cannot follow the old rules of war, which required a raider to stop a merchant vessel, search it, and see its crew safely off before sinking it. A U-boat that surfaced to do this became a fragile target for any armed ship. So Germany embraced 'unrestricted submarine warfare,' sinking without warning, neutral ships included. Militarily it made sense. Politically it was poison, because among the people it drowned were Americans.
1917, the closest run
Germany gambled everything on it. On February 1, 1917, it declared unrestricted warfare and turned its captains loose. The result was staggering. In the first four months of 1917 U-boats sank more than 2.2 million tons of shipping; in April alone they sent nearly 860,000 tons to the bottom, the worst month of the war. One in four merchant ships leaving British ports never returned. At the crisis point Britain was down to a few weeks' supply of food, and its admirals privately doubted they could hold on.
They were saved by an old idea the navy had long resisted: the convoy. Instead of sailing alone, merchant ships crossed in guarded groups escorted by destroyers. A U-boat now had to find a convoy in an empty ocean, then attack through a screen of warships that could hunt it and drop depth charges. Losses fell almost as soon as convoys began in mid-1917, and the crisis passed.
But the gamble had already cost Germany the war in another way. The same campaign that nearly starved Britain also brought the United States, with its factories and its millions of men, into the fight against Germany, a decision the Zimmermann Telegram sealed weeks later. The U-boat had done Germany's arithmetic correctly and its politics fatally. It is the oldest lesson of the weapon, one every navy would relearn a generation later in the same waters: a submarine can sink a nation's ships far more easily than it can win its war.