Habsburg empire Multinational empire in central and eastern Europe, based on the territories of Austria and Hungary. Collapsed at the end of the war in November 1918; officially dissolved in the Treaty of Saint Germain in September 1919.

Haig, Sir Douglas (1861-1928) Commander of the 1st Army Corps of the British Expeditionary Force in France, 1914; succeeded Sir John French as commander-in-chief of British forces in France in December 1915, a position he held until the end of the war - despite his uneasy relationship with Lloyd George. Haig's reputation remains a controversial issue. Seen by some as the 'butcher' behind the bloody Somme and Passchendaele campaigns in 1916 and 1917, others argue that, particularly in 1918, Haig proved himself to be an astute military leader.

Hamid, Abdul (1842-1918) Last sultan of the Ottoman empire, 1876-1909. Known as 'The Great Assassin' for his role in sanctioning the 1894-96 Armenian massacres.

Hamilton, Sir Ian (1853-1947) A close ally of the war secretary Lord Kitchener, Hamilton's appointment as commander of the Gallipoli expedition (1915-16) ended in failure and he was given no further command during the First World War.

Hanna Town on the River Tigris in Mesopotamia, south of Kut-al-Amara and Baghdad. Scene of a failed British attempt to break through the Turkish defensive line on 21 January 1916, during which 2,600 men were killed or wounded.

Hardy, Thomas (1840-1929) English poet and novelist.

Heligoland Bight Small island in the North Sea off the coast of NW Germany. The British Grand Fleet defeated its German counterpart here in the first important naval clash of the First World War on 28 August 1914.

Henderson, Arthur (1863-1935) Led the majority of the Labour Party in supporting the British declaration of war on Germany in August 1914, and subsequently replaced Ramsay MacDonald as leader of the Parliamentary Labour Party. President of Board of Education in Asquith's coalition government, May 1915-December 1916; minister without portfolio in Lloyd George's War Cabinet, December 1916-August 1917.

Hindenburg Line Name given by the British to the Siegfried Stellung (Siegfried Line), after Germany's most famous First World War general, Paul von Hindenburg. Started during the winter of 1916-17, this line of German defensive fortifications stretched from Cerny, east of Soissons, on the Aisne to a point near Beaurains and Neuville Vitasse, just south of Arras.

Hindenburg Programme Programme of German economic mobilisation launched on 31 August 1916 and named after General Paul von Hindenburg. It aimed to double the supply of munitions and triple the output of machine guns and artillery by May 1917.

Household Cavalry The Horse Guards and Life Guards - the cavalry regiments of the sovereign's bodyguard.

Husein, Sherif of Mecca (1856-1931) First king of the Hejaz (Saudi Arabia), 1916-24. Encouraged by T E Lawrence, he led the Arab revolt against Turkey that began in June 1916 and co-operated successfully with the allies in the Middle East during the rest of the First World War.