[7] In August 1914, a flotilla of ten 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.

[9] Due to fears of submarine attack, the Grand Fleet spent much of the first year dispersed on the West coast, while their home base at Scapa Flow had defenses installed.

[11] Because Germany could not possibly deal with British naval strength on an even basis, the German navy was relatively inactive at the start of the war, yet eager to demonstrate a role for itself.

[12] Such views were readily taken up by the German public, as by early 1915, all the combatants had lost the illusion that the war could be won quickly, and began to consider harsher measures in order to gain an advantage.

[14] While the word "blockade" was avoided in official pronouncements, this amounted to unprecedented restrictions on trade with the Central Powers, with even food considered "absolute contraband of war".

[15] The German Chancellor, Theobald von Bethmann Hollweg, felt that such a submarine blockade, based on "shoot without warning", would simply antagonise the United States and other neutrals and have little chance of achieving its objectives.

[17]Von Pohl breached protocol by acting without proper consultation with the Kaiser and the other naval offices, but the Germans were now bound to the strategy to avoid political embarrassment.

[18] In a February 12 directive, von Pohl's replacement as Admiralty Chief Gustav Bachmann however noted that enemy passenger vessels should be deliberately targeted, so as to create a "shock effect".

[7] On 10 April 1915 the British steamer Harpalyce, a Belgian relief ship and clearly marked as such, was torpedoed without warning by SM UB-4 near the North Hinder lightship, just outside the strip of sea declared safe by von Pohl.

The ship had been en route for America to collect food for starving Belgians, and its sinking outraged US citizens already unhappy at the death of Leon C. Thrasher, drowned when U-28 sank Falaba on 28 March 1915.

[26] In the second note Wilson rejected German defenses, rebutting some false claims and asserting that all that mattered was that the Lusitania did not defend herself, but was attacked without warning in such a way that endangered innocent civilian lives.

The third note, of 21 July, issued an ultimatum, to the effect that the US would regard any subsequent sinkings that harm American citizens as "deliberately unfriendly", but signaling an acceptance of submarine warfare under cruiser rules.

[29] The appearance of new minefields off the east coast of Britain in June 1915 puzzled the Royal Navy due to the waters being very busy, and was blamed initially on neutral fishing boats.

When operating in the west, up to the line of Cape Matapan, German U-boats flew the Austrian flag, and a sinking without warning policy was adopted, since large merchant ships could be attacked on the suspicion of being transports or auxiliary cruisers.

This meant a shortage of workers to complete U-boats for service in home waters, but it seemed justified by the successes in the Mediterranean in November, when 44 ships were sunk, for a total of 155,882 tons.

This failure, and the various restrictions imposed on the U-boat Arm in the Atlantic area largely brought the campaign there to a halt, although it continued with little hindrance in the Mediterranean and elsewhere, where there was less likelihood of offending neutrals.

The depth charge, or "dropping mine" as it was initially named, was first mooted in 1910, and developed into practicality when the British Royal Navy's Commander in Chief, Admiral of the Fleet Sir George Callaghan, requested its production in 1914.

Design work was carried out by Herbert Taylor at HMS Vernon Torpedo and Mine School in Portsmouth, England, and the first effective depth charge, the "Type D", became available in January 1916.

Eight of the top dozen U-boat aces served in the Pola flotilla, including the highest scoring commander of all, Lothar von Arnauld de la Perière.

On 31 January, the Kaiser duly signed the order for unrestricted submarine warfare to resume effective 1 February; Bethmann Hollweg, who had opposed the decision, said "Germany is finished".

He was dismayed to be informed by the Admiralty that Germany would win the war if its submarines went unchecked, and cabled Washington to have USN destroyers despatched to Queenstown, Ireland, from where they were to patrol to the west.

When coupled with Germany's policy of unrestricted submarine warfare, the result was that Brazilian ships were soon lost, which drove the country closer to declaring war on the Central Powers.

[60] The Allied Maritime Transport Council was established on 3 November 1917, bringing together representatives from the British Empire, the United States, France and Italy to provide an 'international administration' for more efficient management of shipping.

The Type U-139 were the largest U-boats of World War I. U-151 departed Kiel on 14 April 1918 commanded by Korvettenkapitän Heinrich von Nostitz und Jänckendorff, her mission to attack American shipping.

[66] She returned to Kiel on 20 July 1918 after a 94-day cruise in which she had covered a distance of 10,915 mi (17,566 km), sunk 23 ships totalling 61,000 tons, and had laid mines responsible for the sinking of another 4 vessels.

Though their participation in the conflict was intended as a counter-submarine effort, they were engaged by enemy shore batteries, charted a path through a minefield and helped sink two Austro-Hungarian destroyers at the naval base of Durazzo, Albania.

Beginning in April 1917, Japan, an ally of the United Kingdom, sent a total of 14 destroyers to the Mediterranean with cruiser flagships which were based at Malta and played an important part in escorting convoys to guard them against enemy submarines.

The Allies insisted that an essential precondition of any armistice was that Germany surrender all her submarines, and on 24 October 1918 all German U-boats were ordered to cease offensive operations and return to their home ports.

Overseen by Rear Admiral Sir Reginald Tyrwhitt, commanding officer of the Harwich fleet, the German crews were loaded on to transport ships to be sent home without being allowed to set foot on British soil.

[74] The last significant role played by U-boats in World War I was the suppression of the German naval mutiny that same month, when they stood ready to "fire without warning on any vessel flying the red flag".