At Sea

The years leading up to the war saw the use of improved metallurgical and mechanical techniques to produce larger ships with larger guns and, in reaction, more armour. The launching of HMS Dreadnought (1906) revolutionized battleship construction, leaving many ships obsolete before they were completed. German ambitions brought an Anglo-German naval arms race in which the Imperial German Navy was built up from a small force to the world's most modern and second most powerful. However, even this high-technology navy entered the war with a mix of newer ships and obsolete older ones.

The advantage was in long-range gunnery, and naval battles took place at far greater distances than before. The 1916 Battle of Jutland demonstrated the excellence of German ships and crews, but also showed that the High Seas Fleet was not big enough to challenge openly the British blockade of Germany. It was the only full-scale battle between fleets in the war.

Having the largest surface fleet, the United Kingdom sought to press its advantage. British ships blockaded German ports, hunted down German and Austro-Hungarian ships wherever they might be on the high seas, and supported actions against German colonies. The German surface fleet was largely kept in the North Sea. This situation pushed Germany, in particular, to direct its resources to a new form of naval power: submarines.

Naval mines were deployed in hundreds of thousands, or far greater numbers than in previous wars. Submarines proved surprisingly effective for this purpose. Influence mines were a new development but moored contact mines were the most numerous. They resembled those of the late 19th century, improved so they less often exploded while being laid. The Allies produced enough mines to build the North Sea Mine Barrage to help bottle the Germans into the North Sea, but it was too late to make much difference.


Submarines

Photo of sailors standing on a floating German U-boat U-14.

German U-boat U-14


World War I was the first conflict in which submarines were a serious weapon of war. In the years shortly before the war, the relatively sophisticated propulsion system of diesel power while surfaced and battery power while submerged was introduced. Their armament had similarly improved, but few were in service. Germany had already increased production and quickly built up its U-boat fleet, both for action against British warships and for a counter-blockade of the British Isles. 360 were eventually built. The resulting U-boat Campaign (World War I) destroyed more enemy warships than the High Seas Fleet had, and hampered British war supplies as the more expensive surface fleet had not.

The United Kingdom relied heavily on imports to feed its population and supply its war industry, and the German Navy hoped to blockade and starve Britain using U-boats to attack merchant ships. Lieutenant Otto Weddigen remarked of the second submarine attack of the Great War:

How much they feared our submarines and how wide was the agitation caused by good little U-9 is shown by the English reports that a whole flotilla of German submarines had attacked the cruisers and that this flotilla had approached under cover of the flag of Holland. These reports were absolutely untrue. U-9 was the only submarine on deck, and she flew the flag she still flies – the German naval ensign.

Submarines soon came under persecution by submarine chasers and other small warships using hastily devised anti-submarine weapons. They could not impose an effective blockade while acting under the restrictions of the prize rules and international law of the sea. They resorted to unrestricted submarine warfare, which cost Germany public sympathy in neutral countries and was a factor contributing to the American entry into World War I.

This struggle between German submarines and British countermeasures became known as the "First Battle of the Atlantic". As German submarines became more numerous and effective, the British sought ways to protect their merchant ships. "Q-ships," attack vessels disguised as civilian ships, were one early strategy.

Consolidating merchant ships into convoys protected by one or more armed navy vessels was adopted later in the war. There was initially a great deal of debate about this approach, out of fear that it would provide German U-boats with a wealth of convenient targets. Thanks to the development of active and passive sonar devices, coupled with increasingly deadly anti-submarine weapons, the convoy system reduced British losses to U-boats to a small fraction of their former level.

Holland 602 type submarines and other Allied types were fewer, being unnecessary for the blockade of Germany.