Over the next four decades a number of different submarine designs evolved in various European countries. In the 1880s a really practical design was built in America by an Irish immigrant, John Holland. Originally backed by the Fenian Society (an early North American free Ireland society), it was designed to allow Irish separatists to attack units of the British fleet. In 1900 Holland won a submarine design competition held by the U.S. Navy. From this contract came the USS Holland (SS-1), the first practical combat submarine. The Holland included such innovative features as self-propelled torpedoes fired from a reloadable tube, a battery-powered electric motor for submerged operations, and an advanced hull shape to allow it to move efficiently through the seas. The design was so successful that the U.S. Navy eventually bought a total of seven Holland-designed boats. Ironically, the British even bought some of the Holland boats for the Royal Navy. Holland's company, the Electric Boat Company, continues to build submarines as part of General Dynamics Corporation.
World War I
The period before World War I saw a number of innovations in military submarines. This included the development of diesel engines, improved periscopes and torpedoes, and the development of wireless technology, which allowed them to be directed from shore bases. Within a month of the outbreak of World War I, the German Unterseeboot fleet, or U-boats as they came to be called, were sinking British naval units in the North Sea. In one well-known incident the elderly U-9 sank three British armored cruisers, causing over 1,400 casualties. Throughout the war, both the Allies and the Central Powers took a toll of each other's warships, especially in the Gallipoli Campaign in the Dardanelles.
During World War I the Germans consistently led the world in the production of new U-boats. But the international rules concerning attacks on merchant ships kept the Germans from fully utilizing their potential. Germany feared that unrestricted submarine warfare, with the practice of not warning the victim, might bring the United States into the war. By 1915 the need to isolate Britain from her sources of war supplies caused Kaiser Wilhelm to declare unrestricted submarine warfare an active policy. Soon German submarines were taking a huge toll of merchant shipping and threatening to win the war against Britain all on their own. But after the ocean liner Lusitania was sunk by U-20 in 1915, the United States entered the war on the side of the Allies. It would take two more years for the Allies to win the war and beat back the U-boat threat.
So important was the submarine in World War I that a whole new form of naval conflict, antisubmarine warfare (ASW), was born. From it came techniques such as the convoy and the Q-ship (armed merchant decoy), as well as weapons and sensors such as the antisubmarine detector (ASDIC/sonar), and the depth charge. And so deadly had the U-boats been that Germany was specifically banned from having them under the Treaty of Versailles. The victors of World War I split up the remaining U-boats for examination and testing. That might have been the end of military submarines except that the seeds of World War II were contained in the Treaty of Versailles, and the military submarine would continue to develop.
World War II
During the period between the world wars, submarine development continued at a steady pace. In the United States and Britain efforts were concentrated on the creation of long-range "fleet" submarines designed to support the battle fleets, while nations such as Japan, Russia, and Italy developed submarines more for coastal defense. Once Adolf Hitler had risen to power, Germany secretly began to rebuild its dreaded fleet of U-boats, in direct violation of the Treaty of Versailles. By the beginning of World War II, a number of improvements were made to the submarines themselves, such as torpedoes with magnetic fuses and sonars, and even small radar sets. And in Germany, the United States, and England, naval leaders had evolved very specific plans on how to best use these improvements.
By the outbreak of war in 1939, Germany had deployed her small fleet of U-boats at sea. Within hours, the U-30 sank the ocean liner Athena, signaling another round of unrestricted submarine warfare. Within a few weeks of the opening of hostilities, the U-boats had sunk a number of British warships and merchant vessels. The British responded with a series of patrols by their own fleet of submarines, damaging several German cruisers and sinking several U-boats. In addition, mindful of the damage inflicted upon merchant shipping in World War I, the British immediately instituted a system of transatlantic convoys and began to build up their ASW forces. But German fortunes soared with the capture of France and Norway in 1940, and once these prizes had been won, U-boats could be based much closer to the convoy lanes supplying Britain. The Battle of the Atlantic was on and would not be completely decided until the end of the war in 1945.
The Battle of the Atlantic was a battle of statistics: tonnage and numbers of ships sunk versus numbers of U-boats available and sunk. For Admiral Karl Donitz, the German U-boat commander, it was a battle to get the greatest number of U-boats possible out onto the convoy routes. To do this he implemented what were called wolf pack tactics, setting a large number (ten to fifteen) of U-boats onto a convoy all at the same time. For a while, particularly during 1941 and 1942, the tac-tics worked. No less a figure than Sir Winston Churchill was reported to have said, "The only thing that truly worried me was the U-boat menace." He had much to be worried about, for Admiral Donitz's U-boat force almost won the war by starving Great Britain into submission.
The British fought back though, using advanced tactics and equipment such as radar, escort corvettes, and frigates, and developing the small escort carrier.
In addition, the British had the ultimate secret weapon, Ultra. Ultra was the British program to penetrate German command communications, protected by the Enigma cipher system. Early in the war, with valuable contributions from the Poles and the French, England began to read an ever-growing flow of German messages. By 1941, through a combination of incredible technical analysis and outright theft of German cipher key books and captured Enigma equipment, the British were able to read virtually every message sent and received by the U-boats. Ultra allowed the British to route their convoys around known wolf packs and to start aggressively hunting the U-boats with aircraft and so-called hunter-killer groups. By 1943 the balance had turned decisively in favor of the Allies. Despite a number of German innovations such as the snorkel, homing torpedoes, and antisonar coatings, the battle was eventually won by the Allies.
In the Pacific, submarines actually won a major campaign against merchant shipping. In December 1941 Imperial Japan initiated a war of conquest against the Allies. At the start, things went very poorly for the United States. With most of their battleship force sunk or out of action after the bombing of Pearl Harbor, the only way the Americans could strike back was with their well-developed force of fleet submarines. It took a while to get rolling, especially when eighteen months were needed to repair a series of faults with the American Mark 14 torpedo and its magnetic fuse, but by late 1943 the American subs were beginning to make a real difference in the amount of material getting to Japan's war industries. Under the command of Admiral Charles Lockwood, the American boats were starting to starve Japan into submission. In addition, they were taking an increasing toll of Japanese warships.