Submarine Warfare in World War I

WWI U-boat sinking a tramp freighter

After the enormous battleship buildup prior to WWI, the great fleets adopted play-it-safe tactics once war began. This came as a distinct anticlimax to a public expecting a new Battle of Trafalgar -- a decisive showdown on the high seas that would decide the war in an afternoon. Following the cruiser clashes and battlecruiser brushes of 1914-15, there came a lull coinciding with the tenure of Adm. Hugo von Pohl as German C-in-C. During this time there was no indication a full-blown fleet action might be imminent. The battle fleets settled into a pattern of distant blockade by the British and occasional jabs at small, undefended English ports by the fast-moving German battlecruisers. Even after the furious but indecisive Battle of Jutland in May 1916 -- especially after Jutland -- the rivalry between the British and German dreadnought fleets was no nearer resolution. Despite its horrific costs, Jutland only reinforced the status quo: a 3:5 ratio of superiority in favor of the British, significantly higher than the 2:3 margin sought by the Germans in the prewar arms race. The long-distance standoff continued, with the Germans increasingly immobilized by wartime coal shortages and the related habit of keeping the fleet in port.

WWI German fleet in port

The High Seas Fleet blockaded in port at Wilhelmshaven.

But Germany actually came close to winning the war at sea through a cheaper, sneakier weapon: the U-boat. Despite the persistent exhortations of Jacky Fisher to develop a strong Royal Navy submarine arm, the British regarded the submarine as "underhanded, unfair, and dashed un-English." The Admiralty responded to Fisher's emphatic memorials by developing the K class, an oil-burning steam-and-electric-powered giant submarine, with elaborate snorkel funnels to carry off smoke while operating awash or slightly submerged. These 339-foot, 2500-ton (submerged displacement) vessels were designed to maneuver in unison with the fleet like flotillas of torpedo boats; predictably, the K-boats proved a costly fiasco, capable of 24 kts in calm seas but unable to keep up with surface ships in weather. Predictably, they suffered from multiple, often deadly technical failures. The German U-boats, by contrast, were more straightforward technically, and proved capable of performing a more circumscribed mission quite reliably. Early models used kerosene engines on the surface, leaving a tower of oily smoke visible for miles, leading to British overconfidence about their ability to crush the U-boat threat. In 1913 Germany started installing diesel engines as the standard surface power plant in all its U-boats. The diesel generally ran without emitting telltale exhaust; the British were in for a surprise. Initially, the U.S., Russia, and Sweden had pioneered sub technology; Germany shared Britain's disdain for the submarine until forced to reconsider it after 1914.

WWI German U-boat running on the surface

Above, U-45, a German Type IV boat built in 1913. Driven by diesel engines while surfaced and electric motors when submerged, this craft was typical of Germany's commerce raiders in WWI, though several longer-range models were built later in the War, as were specialized submarines such as the 136 UB and UC boats -- submarine minelayers of 130 to 520 tons--, or the 1,500-ton "merchant submarine" Deutschland which crossed to America several times during the War. To begin with, the Allies greatly underestimated the range and destructiveness of the submarine. Confronted by slow economic strangulation and with their battleship strength at only 60% that of the British, the Germans turned to U-boat warfare in desperation, little guessing at first how close it would come to turning the tide for them. When Britain declared a total blockade of Germany late in 1914, high-handedly invoking the threat of starvation should the War be prolonged, the Germans retaliated by declaring the seas around the British Isles to be a submarine warfare zone -- never mind they had only eight or nine long-range subs available at any one time to patrol Britain's western approaches.

Illustrtion of British steamer being evacuated by U-boat crew on stormy grey sea, by Willy StoewerAlthough surprise attacks on enemy warships were fair game in time of war, the position with regard to enemy commerce was murkier. The U-boat occupied an anomalous position in international law. Under the "Cruiser Rules" which governed commerce raiding in war, a commerce raider encountering an enemy ship would stop it -- if necessary by putting a shot across its bows -- and inspect its papers. If it proved an enemy flagged vessel, its crew and passengers would be allowed to gather possessions and provisions and escape in the lifeboats. The U-boat commander might also make other provision for their safety before destroying the vessel or sailing it into port as a prize of war. To follow this procedure (as most U-boat captains did at the beginnning of the War) was to throw away a U-boat's main advantage. A sub's chief weapon was surprise -- invisibility; but it was slow-moving and highly vulnerable to attack while surfaced and stopped. After losing merchant vessels to submarine attack the British Admiralty began arming cargo ships and liners. In early 1915, British skippers were instructed to run down submarines and sink them by collision. Several U-boats were dispatched by ramming or fell victim to sudden attack by nearby cruisers while surfaced. In response, the German admiralty ordered stealth torpedo attacks without warning.

Cutaway diagram of a WWI Schwartzkopff torpedo

For this purpose, the U-boat's weapon was the locomotive torpedo. Originally developed in the late 1860s by the Englishman Robert Whitehead at labs in the Adriatic, and first used in combat in the 1870s, Whitehead torpedoes had been perfected for active service in the mid-1890s. Their range and size had improved steadily since. Propelled by compressed air, stabilized by gyroscopic mechanisms, packing 200 lbs of TNT in its deadly warhead, the WWI period Schwartzkopff torpedo (shown above) was a high-tech weapon of its day. Although a large percentage of German torpedoes early in the War were duds, those that did ignite proved their potency. Lightly built merchant ships could be crippled or sunk with one hit, though sometimes a U-boat would have to surface and finish off a slow-sinking victim by shelling it at the waterline with the sub's deck gun. As the war dragged on, torpedo accuracy and reliability improved with practice.

U-boat control room during attack: WWI-era illustrationTo the painful surprise of the Allies, the U-boat proved the Kaiser's most fearsome weapon by sea. Only weeks into the War came the scandalous sinking of 3 Bacchante-class cruisers, dubbed the Live Bait Squadron after the event (~1450 killed); soon afterwards, a sub in the Channel destroyed the pre-dreadnought battleship HMS Formidable (~550 lost); then in May 1915 came the Lusitania affair, in which a single torpedo from the U-20 sank one of the largest, fastest liners afloat in 18 minutes flat. 1,198 lost their lives in a dèbacle that compared unfavorably with the Titanic's demise only 3 years before. While 128 Americans died in the Lusitania disaster, most of the American people still opposed involvement in the European conflict, and U.S. diplomacy with Germany was remarkably mild at first, reflecting the pacifist beliefs of Secretary of State William Jennings Bryan. The post-Lusitania uproar in Britain and America pressured the Kaiser to restrict his subs temporarily; but the need to shorten the war soon prevailed and Germany resumed unrestricted submarine warfare in March 1917. The U-boats began hunting and killing with a vengeance, seriously threatening Britain's abilityto sustain her heroic war effort, and sinking scores of neutral American ships in the process. While the proximate cause of the United States' entering the war was the Zimmermann Telegram (in which Germany urged Mexico to join a war of conquest on the U.S. and share the spoils of victory), the Lusitania tragedy, the mounting losses in shipping, and repeated evidence of German bad faith all set the American climate for war. To this day, the U.S. State Department website erroneously cites unrestricted submarine warfare as America's sole cause for war with Germany in WWI.

US destroyers arriving in Irish waters, 1917Typically operating alone and far from base for weeks at a time, most German commerce-raiding subs at war's end were 240-foot, 820-ton models carrying a 4.1" gun and 16 torpedoes with 6 tubes for launching. They were sinking a steadily rising percentage of cargos inbound to Britain and France starting in February 1917, and threatening troop transports as well. At the start of the unrestricted submarine campaign in early 1917, U-boats were sinking more than 500,000 tons of shipping a month (versus 790,000 tons in total sunk between August 1914 and Sept. 1915). April 1917's monthly total topped 850,000 tons -- the wartime high. Because Lord Fisher had initiated an ill-advised crash capital ship construction program, British yards were unable to replace the tonnage destroyed. By 1918, Germany alone had 135 U-boats in commission; Austria-Hungary a further 21 subs (also called U-boats in the Austro-Hungarian Kriegsmarine). Germany shared basing facilities at Pola, Kotor, and Istanbul with her Central Powers allies, enabling her to wage devastating warfare in the Mediterranean right through the end of 1918. On the Atlantic, only the convoy system devised by U.S. Admiral William S. Sims and Britain's First Sea Lord Sir John Jellicoe foiled the go-for-broke U-boat offensive in the final year of the War. Convoys served as magnets for hunting subs, luring them under concentrated formations of antisubmarine warships (ASW). Working in teams, destroyers and light escort vessels used primitive sonar ("hydrophones") and knowledge of their enemy's tactics to locate and destroy U-boats. Together they developed depth charges and techniques of ASW that stood the Allies in good stead when they faced an even more dire U-boat threat in WWII. Gone were the singleton steamers that had provided such fat pickings for the U-boats before convoys became mandatory.

In all, 123 U-boats were destroyed by the new weapons in the last two years of the Great War. With new U-boat production at a plodding six per month, Germany could no longer make up her losses in subs and crews. By upping production of merchant ships and blunting the U-boat threat, the Allies turned the war of attrition back on Germany. Allied shipping losses stabilized at acceptable levels, while U-boat effectiveness plummeted.

It had been a near thing, though. German complacency and naval conservatism had assisted the Allies no end. For instance, in early 1917 a far-sighted U-boat skipper, Cmdr. Hermann Bauer, suggested greater coordination of attacks. Under his plan, giant subs would comb the ocean, acting as mobile radio stations, transmitting target information to hunting groups of U-boats -- a precursor to the dreaded "wolf packs" of WWII. For his pains, Bauer was relieved of command and exiled to a remote desk where no telephone sat and no work was provided. Meanwhile, the decision to accelerate U-boat production lagged until Oct. 1918, when the War was already irretrievably lost; German shipyards were occupied with building eight new dreadnoughts. None of these was completed by war's end. With such groupthink in the saddle, Germany deserved to lose the naval war.

Liberty Loan Poster feat. U-boat

The moral issue of the U-boat war and Allied success in antisubmarine warfare (ASW) are touched on by this wartime poster touting war bonds. While the image is admirably composed, the artist has taken considerable liberties with the colors of the destroyer's dazzle-pattern camouflage paint -- an experimental anti-submarine measure adopted later in the War. Actual camouflage colors were shades of blue, grey and black, though many patterns were much more bizarre than that seen here. The big liner, too, would have been painted in dazzle colors during hostilities.

No essay on WWI submarining would be complete without a tip of the hat to the British submarine service. From The time of the Gallipoli invasion to the the Allied intervention in the Russian civil war, from the Black Sea to the Baltic, or to the Med, British submarine commanders compiled an admirable record in offensive warfare. Watch our site for a new page of British submariner's exploits in the Great War!

Whatever may be said about the morality of submarine sneak attack, it packed a wallop. Allied losses to U-boats totaled some 5,000 freighters, tankers, and sailing ships -- in all, an astounding 11 million tons of shipping sent to the bottom in WWI. More than 15,000 British civilians lost their lives due to U-boat attack. Hear an American sailor, Ray Millholland, on the wreckage left behind by sinkings in the Mediterranean in 1918:

Everywhere on the surface . . . extending as far as the circular horizon, was mute evidence of the effectiveness of Germany's unrestricted submarine campaign. We were constantly shifting our zigzag course to avoid smashed lifeboats, drifting hatch gratings, and the odd clutter of gear that rises to the surface from a sunken ship. Occasionally a shapeless uhdulating mass buoyed by a cork life jacket would drift by, and a brine bleached face would stare with empty eye sockets at the glaring sun.

As for the German submarine service, its mortality of 4,849 exceeded 40 percent of its personnel. May they all rest in peace.

WWI German U-boat surfacing
A WWI U-boat surfaces in the North Atlantic. Zigzag device on bow is a blade for cutting submarine nets.

Relevant Weblinks:

c1895 Whitehead torpedoPre-WWI Schwartzkopff Torpedo adc1895 Whitehead torpedo



HMS AUDACIOUS sinking after hitting a mine, 1914

German cruisers laying mines at night, WWIAfter the sub-launched torpedo, the straightforward, inexpensive mine proved the most lethal weapon at sea in WWI. At top, the brand-new superdreadnought Audacious gradually succumbs after striking a mine off Ireland in 1914. So stiff was this blow that the Admiralty did not acknowledge the loss until after the Armistice 4 years later, keeping Audacious on the books with an assigned commander and signal-log until that time! Not far from there, off Cape Wrath, Scotland, the pre-dreadnought battleship King Edward VII was mined and sunk the following year, the lethal device originating from the famous German raider Möwe in this case. Floating explosive devices had a long history already by this time; river ironclads such as the USS Cairo were destroyed by primitive mines in the American Civil War, when they were called torpedoes: Adm. Farragut's famous line "Damn the torpedoes! Full speed ahead!" referred to the minefields at the entrance to Mobile Bay. The oft-quote words were spoken after his ironclad monitor Tecumseh was sunk by one of the deadly devices, when some of his captains showed signs of unsteady nerves. Forty years later in the Russo-Japanese War, the Japanese lost two of their six battleships to Russian mines, while the Russians lost their best commander when Japanese mines blew up and sank his flagship Petropavlovsk in about two minutes flat, with an appalling loss of life. Less dramatically, but just as surely affecting the outcome, numerous big ships on both sides were disabled and removed from the fight by mine damage.

Contact mine, WWIIn the First World War, minelayers and minesweepers were busy from the North Sea to Baltic, from the Adriatic to the Bosporus; at left, crewmen sow mines by pushing them down a track and out special doors in the stern of a cruiser modified for minelaying. Huge minefields in the Heligoland Bight protected the chief German base at Wilhelmshaven and the great British bases at Portsmouth and Scapa Flow, plus the many smaller ones. It is estimated that 190,000 mines were deployed in the North Sea-English Channel-Heligoland naval war zone during the Great War. All sides also developed smaller submarines specifically designed for mining shipping lanes. The commonest (and cheapest) form of mine used was the contact mine. A typical contact mine was a spherical or cylindrical container containing between 125 and 1,400 kg of explosives (275 to 3,090 pounds), detonated when a ship bumped into one of the mine's horns. These protruding knobs, known as Hertz horns or chemical horns, were invented in the 1870s. Encased in a lead tube, they each contained a glass vial of sulfuric acid. When the vial was fractured by contact with a ship hull or other object, the acid dripped onto a lead-acid battery within the mine armature, generating an electric current that detonated the explosives. If properly placed this chemical reaction could blow a 25-to-40-foot hole in a ship's side. One or more such explosions could doom a ship. Even if the damage were not fatal, it could take the ship out of service for a prolonged period. WWI was the high tide of mine warfare. It has been estimated that 235,000 sea mines were deployed during the war.

Dozens of warships and hundreds of merchant craft fell victim to mining in WWI. Perhaps the greatest massacre inflicted by mines was the ill-fated attempt by the Allies to force the Dardanelles on March 18, 1915. That day three pre-dreadnought battleships were sunk, two more seriously damaged, and the dreadnought battlecruiser Inflexible also badly damaged; the French battleship Bouvet (included in the tally above) sank in less than one minute with her captain and 639 hands after a mine detonated one of her magazines (66 were saved). Mines were just as merciless to ships of the Central Powers: The dreadnought Goeben, transferred to the Ottoman navy in 1914 and renamed Yavuz, had several encounters with mines, most prominently her return from the attack on Imbros in January 1918. Yavuz spent some anxious days beached on a sandbar inside the Dardanelles for emergency patching before proceeding to Istanbul under tow. Yavuz' consort, the light cruiser Breslau, was not so lucky, exploding five contact mines over two days and sinking with 93% of her crew; the battlecruiser detonated three mines while attemping to assist the Breslau, her companion in many fights and operations over a four-year span. The damage to Yavuz was patched up hastily at Sevastopol during its mid-1918 German occupation, but the battlecruiser was not completely repaired until an overhaul ten years later.

Interior of minelayer - mine deckAt right, the interior of a minelayer, with lines of mines all set for laying. Crewmen worked under an eerie deep-blue light to maintain their night vision. Thanks to its economy and effectiveness, the marine mine continued its depradations into WWII and beyond. In fact, the official Soviet government story has it that a Nazi-laid mine in the Black Sea claimed one of their war prizes -- the battleship Novorossisk. This was the name with which Stalin dubbed the 1914 Italian dreadnought Giulio Cesare when she was assigned to the USSR as war reparations in 1946. The old vessel blew up and sank in her namesake port in 1954, placing her (with her sister Andrea Doria and the Turkish Yavuz, ex-Goeben) among the longest-lived WWI dreadnoughts. If true, the official Kremlin story would make this mine a wonder of surviving function -- it would have spent 11 or 12 years in seawater before devastating a warship that was also "of an age." Yet this is not impossible. Errant WWII mines have been documented exploding more than 60 years after manufacture. Conspiracy theorists have an alternate explanation: In an act of vengeance for the Russians' taking their prized battleship, mysterious Italian frogmen sabotaged the ship's hull by dark of night, escaping before the time-activated explosives devastated the target. Italian frogmen indeed did just this with the Austrian battleships Viribus Unitis and Wien in WWI; repeating the feat against HMS Queen Elizabeth and Valiant in Alexandria Harbour during WWII. But hard evidence of an Italian commando caper in the USSR in 1954 is hard to come by. It is perhaps telling that no fresh information came out between the fall of the secretive, paranoid Soviet regime in 1991 and the rise of the secretive Putin regime after 2000.

An Undersea Gallery of Mine Images

Illustration of pre-dreadnoughts in a minefield


German contact mines, 1914
Contact mines splash into the sea from a speeding minelayer, cupped in cradles that form a weighted anchor for the mines.

Mines aboard an Italian minelayer
The mines deploy automatically. Tether wire unrolls to float mines at a pre-set depth.

Diagram of Mine Deployemnt
The sprouting of mines from their bases is shown. It's easy to see why the process was called "planting mines."

Mine exploding - huge tower of spray
A forceful mine detonation shows why these explosive devices commanded such fear.

Hole in battleship's hull caused by a mine, 1916

The result of one such detonation: This photo of the German super-dreadnought Baden after her 1917 encounter with a Russian mine, documents the devastating nature of mine damage.

Ship in dock with stern blown off by mine

Mine damage to the Turkish gunboat Malatya, which lost her stern. Ugly as this mangled mass of metal is, Malatya was lucky: had she made contact amidships, the whole ship likely would have been lost.

Hole in frigate's hull caused by a mine, 1988

The mine remains deadly today: Damage to the U.S. guided missile frigate Samuel F. Roberts (FFG-58), mined Apr. 14, 1988 during the U.S. intervention in the Iran-Iraq War on the side of Saddam Hussein -- the largest USN deployment since WWII. Explosion wounded ten sailors, dismounted the ship's gas-turbine engines, and broke her keel. Five hours' desperate damage control saved the four-year-old ship, but the Roberts' damage took 13 months to repair. The cost of repairs exceeded US $89.5M; cost of the mine to Iran: a mere $1,500.

Naval mine test, ship detonating mine.
Photo of a test: lifting action amidships demonstrates why mines broke the backs of so many ships.


Map of minefields in the North Sea, 1918

Extent of minefields deployed by the Allies in the North Sea, 1918. Early model British mines were a failure; in Nov. 1917 the H-2, a faithful copy of the deadly German marine mine, became widely available and the minefields shown were sown. In all 235,000 marine mines were deployed during the war; some 165,000 are represented here. Known as the Great North Sea Mine Barrage, the vast boom between Scotland and Norway was constructed by an enthusiastic U.S. Navy. 70,263 Mark IV mines -- produced in Detroit by a retooled auto industry -- were laid in a 3-D grid across the sea. U-boat crews had to dodge through the barriers on departure and homecoming. Six subs were known to be destroyed by mines in these fields; in addition, some U-boats became entangled in net obstructions and drowned, unable to escape or surface. American historian and onetime arms negotiator Robert L. O'Connell comments: "... a very unpleasant antidote to a very unpleasant weapon ... In the 20th century, technology did not just kill, it killed with flair and imagination."
--  O'Connell, Sacred Vessels: The Cult of the Battleship and the Rise of the U.S. Navy (Oxford: Westview Press, 1991), 223.


Mines aboard an Italian minelayer
A deckload of mines ready to roll down the minelayer's rails and into the sea. Italian navy, WWI.

Spanish contact mine, 1898
Contact mine, fished out after fouling one of the USS Texas' propellers in 1898.
Its detonators were fouled by barnacles and weed growth, rendering it ineffective.
Behind mine is one of Texas' 6"/35 (152 mm) Mark 4 guns in an Armstrong shielded mount.