The U-boat Campaign from 1914 to 1918 was the World War I naval campaign fought by German U-boats against the trade routes of the Allies.
It took place largely in the seas around the British Isles and in the Mediterranean.
The German Empire relied on imports for food and domestic food production (especially fertilizer) and the United Kingdom relied heavily on imports to feed its population, and both required raw materials to supply their war industry; the powers aimed, therefore, to blockade one another.
The British had the Royal Navy which was superior in numbers and could operate on most of the world’s oceans because of the British Empire, whereas the Imperial German Navy surface fleet was mainly restricted to the German Bight, and used commerce raiders and unrestricted submarine warfare to operate elsewhere.
In the course of events in the Atlantic alone, German U-boats sank almost 5,000 ships with nearly 13 million gross register tonnage, losing 178 boats and about 5,000 men in combat.
Other naval theatres saw U-boats operating in both the Far East and South East Asia, the Indian Ocean and the Mediterranean and North Seas.
In August 1914, a flotilla of nine U-boats sailed from their base in Heligoland to attack Royal Navy warships in the North Sea in the first submarine war patrol in history.
Their aim was to sink capital ships of the British Grand Fleet, and so reduce the Grand Fleet’s numerical superiority over the German High Seas Fleet.
The first sortie was not a success.
Only one attack was carried out when U-15 fired a torpedo (which missed) at HMS Monarch. Two of the ten U-boats were lost.
Later in the month, the U-boats achieved success, when U-21 sank the cruiser HMS Pathfinder.
In September, SM U-9 sank three armoured cruisers (Aboukir, Hogue, and Cressy) in a single action.
Other successes followed. In October U-9 sank the cruiser Hawke, and on the last day of the year, SM U-24 sank the pre-dreadnought battleship Formidably.
By the end of the initial campaign, the U-boats had sunk nine warships while losing five of their own number.
Mediterranean: Initial stage Main article: Mediterranean U-boat Campaign (World War I) The initial phase of the U-boat campaign in the Mediterranean comprised the actions by the Austro-Hungarian Navy’s U-boat force against the French, who were blockading the Straits of Otranto.
At the start of hostilities, the Austro-Hungarian Navy had seven U-boats in commission; five operational, two training; all were of the coastal type, with limited range and endurance, suitable for operation in the Adriatic. Nevertheless, they had a number of successes.
On 21 December 1914 U-12 torpedoed the French battleship, Jean Bart, causing her to retire, and on 27 April 1915 U-5 sank the French cruiser Léon Gambetta, with a heavy loss of life. But the Austro-Hungarian boats were unable to offer any interference to allied traffic in the Mediterranean beyond the Straits of Otranto.
Submarine warfare In 1914 the U-boat’s chief advantage was to submerge; surface ships had no means to detect a submarine underwater, and no means to attack even if they could, while in the torpedo the U-boat had a weapon that could sink an armoured warship with one shot.
Its disadvantages were less obvious but became apparent during the campaign.
While submerged the U-boat was virtually blind and immobile; boats of this era had limited underwater speed and endurance, so needed to be in position before an attack took place, while even on the surface their speed (around 15 knots) was less than the cruising speed of most warships and two thirds that of the most modern dreadnoughts.
The U-boats scored a number of impressive successes and were able to drive the Grand Fleet from its base in search of a safe anchorage, but the German Navy was unable to erode the Grand Fleet’s advantage as hoped.
Also, in the two main surface actions of this period, the U-boat was unable to have any effect; the High Seas Fleet was unable to draw the Grand Fleet into a U-boat trap.
Whilst warships were travelling at speed and on an erratic zigzag course they were relatively safe, and for the remainder of the war the U-boats were unable to mount a successful attack on a warship travelling in this manner
First attacks on merchant ships The first attacks on merchant ships had started in October 1914. At that time there was no plan for a concerted U-boat offensive against Allied trade.
It was recognised the U-boat had several drawbacks as a commerce raider, and such a campaign risked alienating neutral opinion.
In the six months to the opening of the commerce war in February 1915, U-boats had sunk 19 ships,