|In Command||Rear-Admiral Commanding, Harwich Force|
|First||Rear-Admiral Reginald Y. Tyrwhitt|
|Last||Rear-Admiral George H. Borrett|
After the outbreak of the First World War, a priority for the Royal Navy was to secure the approaches to the English Channel, to prevent elements of the German High Seas Fleet from breaking out into the Atlantic, or from interfering with British maritime trade and convoys to the continent. Most of the major fleet units of the Grand Fleet had dispersed to the navy's anchorage at Scapa Flow or to other North Eastern ports to monitor the northern route from the North Sea into the Atlantic. Consequently, a number of patrol flotillas were organised along the south and east coasts of England, with commands established at several of the major ports in the region. The Dover Patrol was based at Dover, consisting mostly of destroyers, while a number of pre-dreadnoughts and cruisers were based at Portland Harbour. A large number of destroyers, flotilla leaders and light cruisers were centred at Harwich, under the command of Commodore Reginald Tyrwhitt.
It was intended that the Harwich Force would operate when possible in conjunction with the Dover Patrol, and the Admiralty intended that the Harwich force would also be able to support the Grand Fleet if it moved into the area. Tyrwhitt was also expected to carry out reconnaissance of German naval activities in the southern parts of the North Sea, and to escort ships sailing between the Thames and the Netherlands. Tyrwhitt's objectives were often complicated by the need to provide reinforcements for the Dover Patrol. The force fired the first shots of the war when a flotilla led by Template:Ship sank the minelayer Template:Ship on 5 August 1914. During the war, the Force captured or sank 24 enemy merchants, and it escorted 520 eastbound and 511 westbound ships between Dutch and British ports. Their ships also took part in the Cuxhaven Raid on Christmas Day, 1914.
The force was also active in a number of clashes with the Kaiserliche Marine (German Navy). Their ships were present at the Battles of Heligoland Bight, Texel, and Dogger Bank, and were mobilised after the German raids on Scarborough, Hartlepool and Whitby in 1914, and on Yarmouth and Lowestoft in 1916. They were called out during the lead up to the Battle of Jutland, but did not take part in the battle.
During the winter of 1916-1917, the force assisted the Dover Patrol in patrolling the Dover Barrage, an anti-submarine steel netting barrier which required on a large number of small vessels to operate and were vulnerable to attack by German destroyers and torpedo boats. Other regular patrols were mounted in The Downs, an anchorage in the eastern part of the Channel, and another net barrage which was laid parallel to the Belgian coast. Forays along the coast of Germany sometimes resulted in the sinking or capture of German fishing vessels; on one sweep in 1915, twenty captured trawlers were brought to Harwich as prizes. Another duty was coastal bombardment of German positions in occupied Belgium; on one mission to bombard Ostend on 5 June 1917, Tyrwhitt's flagship, Template:Ship, sank the German torpedo boat S.20 off Zeebrugge.
After the end of the war, Harwich was designated the port at which the remaining German U-boats would be surrendered, and Tyrwhitt's Harwich Force oversaw the operation. The Harwich Force consisted of between four and eight light cruisers, several flotilla leaders and usually between 30 and 40 destroyers, with numbers fluctuating throughout the war, and organised into flotillas. Also stationed at Harwich was a submarine force under Commodore Roger Keyes.
In early 1917, the Harwich Force consisted of eight light cruisers, two flotilla leaders and 45 destroyers. By the end of the year, there were nine light cruisers, four flotilla leaders and 24 destroyers. The combination of light, fast ships was intended to provide effective scouting and reconnaissance, whilst still being able to engage German light forces, and to frustrate attempts at minelaying in the Channel.
Rear-Admiral Commanding, Harwich Force
- Rear-Admiral Reginald Y. Tyrwhitt, 27 April, 1914 – 1 May, 1919.
- Rear-Admiral George H. Borrett, 1 March, 1919 – 23 August, 1919.
- Jellicoe, Viscount Jellicoe Of Scapa (1920). The crisis of the naval war.
- Tucker, Spencer (2005). World War I: Encyclopedia. ABC-CLIO. ISBN 1-85109-420-2.
- King-Hall, Stephen (1929). The War on Sea: 1914–1918. London: Ernest Benn Limited.
- Massie, R. K. (2004). Castles of Steel: Britain, Germany and the Winning of the Great War at Sea. New York: Ballantine Books. ISBN 978-0-345-40878-5.
- The Admiralty (1920). Battle of Jutland, 30th May to 1st June 1916: Official Despatches with Appendices. London: H.M. Stationer