Imperial War Cabinet Body created by the British prime minister David Lloyd George in the spring of 1917 to bring into the Allied policy-making process his counterparts in Australia, Canada, New Zealand and South Africa, as well as the secretary of state for India.

Imperial War Graves Commission Created by Royal Charter on 21 May 1917. Charged with marking and maintaining the graves of all the fallen members of the British empire's armed forces and creating cemeteries and memorials in their honour. Known today as the Commonwealth War Graves Commission.

Indefatigable One of three British battle cruisers sunk by the German naval fleet at the Battle of Jutland (31 May-1 June 1916).

Independent Labour Party (ILP) Founded in Bradford in 1893, the ILP was the largest political party in Britain to oppose the First World War. Many of its activists were prominent in the anti-conscription campaign that began in 1915.

Indian Army From a pre-war strength of 155,000, the Indian Army rose in size to 573,000 men by November 1918. Most of the 1.3 million men who served in it during the First World War were Indians, though the officer corps was largely British. They saw action in particularly large numbers on the Western Front and in Mesopotamia.

Influenza pandemic Worldwide epidemic of the disease also known as 'Spanish flu'. Killed as many as 30 million people between 1918 and 1920.

Information, Ministry of Created in February 1918 under Lord Beaverbrook, the last new ministry to be created during the First World War. Discontinued in November 1918.

Invincible One of three British battle cruisers sunk by the German naval fleet at the Battle of Jutland (31 May-1 June 1916).

Ironside, General William Edmund (1880-1959) Served on the Western Front throughout the First World War and as commander-in-chief of the British forces sent to support the counter-revolutionary 'Whites' in Russia, 1918-19. During the Second World War, he was commander-in-chief of the British home forces.

Isonzo River in SE Europe, rising in NW Slovenia and flowing into NE Italy. During the First World War, the Isonzo valley was the scene of no fewer than 12 battles between Italian and Austro-Hungarian forces. The final one in October 1917, better known as the Battle of Caporetto, resulted in a humiliating defeat for Italy that nearly drove it out of the war.