Field Marshal Sir Douglas Haig replaces Field Marshal Sir John French as commander of the British Expeditionary Force (BEF).
The Germans use phosgene gas for the first time against the British at Wieltje, near Ypres.
The Ottomans besiege British-Indian forces at Kut in Mesopotamia (now Iraq).
The Battle of Kosturino on the Salonika front ends in a Bulgarian victory over the Allies.
The Short Magazine Lee Enfield (SMLE) Mk III*, a cheaper mass-produced version of the British Empire’s iconic Mk III Rifle (adopted in 1907), is introduced for general service.
The Serbians are defeated by the invading Central Powers and remnants of their army are evacuated by Allied navies to regroup.
The Battle of Ctesiphon, fought between British and Ottomans forces in Mesopotamia (now Iraq), is inconclusive.
Senussi tribesmen, backed by the Ottomans, rise up against the Allies in Italian Libya and Egypt. Although suppressed by the British, the revolt rumbles on until 1917.
The British Army forms the Machine Gun Corps to make more effective use of heavy machine guns (primarily the Vickers) on the Western Front.
Serbia is invaded by Germany, Austria-Hungary and their new ally, Bulgaria.
French, British and Italian troops begin landing at Salonika (now Thessaloniki, in Greece) in the Balkans.
The British Army officially adopts the Lewis Gun for both land and aircraft use.
Following victory at Es Sinn, British-Indian forces capture the town of Kut in Mesopotamia (now Iraq) from Ottoman forces.
The Battle of Es Sinn ends in a British-Indian victory over the Ottomans in Mesopotamia (now Iraq).
The Battle of Loos on the Western Front sees the British offensive fail at German hands. The 50-watt Trench Set (or BF Set), the British Army’s first reliable radio, was first used during this engagement.
The Russian Tsar Nicholas II replaces Grand Duke Nicholas Nikolayevich as Commander-in-Chief of the Russian Army.
The British Army adopts the Brodie helmet as its standard head protection for soldiers.
The last attempt by the British to seize the Gallipoli peninsula is unsuccessful.
The Indian Army defeats a series of tribal uprisings in the Swat Valley on the North-West Frontier of India (now in Pakistan).
Part of the Gallipoli Campaign: The Battle of Chunuk Bair at Anzac Cove ends in an Ottoman victory.
Part of the Gallipoli Campaign: The Battle of the Nek at Anzac Cove ends in an Australian defeat.
Part of the Gallipoli Campaign: The Battle of Sari Bair follows new landings at Suvla.
Part of the Gallipoli Campaign: The Battle of Lone Pine ends in an Australian victory.
Pope Benedict XV appeals to all governments to cease hostilities.
British-Indian forces defeat the Ottomans at Shaikh Othman near Aden.
The German forces in South-West Africa (now Namibia) surrender at Khorab.
Ottoman forces secure victory over the British at Lahij near Aden.
The Royal Engineers form Special Companies to oversee Britain’s gas warfare effort.
A German Fokker, the first aircraft to be fitted with a device enabling the pilot to fire his machine gun through the arc of the propeller, shoots down a French aircraft.
The first large-scale use of flamethrowers takes place at Hooge in Belgium, during a German attack on the British lines.
Part of the Gallipoli Campaign: The Battle of Gully Ravine at Cape Helles secures limited British gains.
Fighting takes place between the Italians and Austro-Hungarians along the Isonzo (now the Soča) valley. A total of 12 battles are fought in this location, wearing down the armies of both nations over the following two years.
Part of the Gallipoli Campaign: The Third Battle of Krithia fails to secure an Allied breakout.
The Maudsley Military Hospital is set up in London to treat cases of shell shock (neurasthenia).
The Battle of Festubert on the Western Front secures limited British gains at German expense.
Windhoek, the capital of German South-West Africa (now Namibia), is occupied by South African troops.
A British offensive at Aubers Ridge on the Western Front ends in a German victory.
The British liner ‘Lusitania‘ is sunk off the south coast of Ireland by a German U-boat. The loss of over 120 American lives causes a storm of protest in the United States.
Part of the Gallipoli Campaign: The Second Battle of Krithia results in an Allied failure at the hands of the Ottomans.
The No 5 Grenade (Mills Bomb) is introduced. This is the standard grenade used by British Empire forces for the rest of the war.
Part of the Gallipoli Campaign: The First Battle of Krithia sees the Allied advance repelled by the Ottomans.
The Allies offer Italy territorial gains in any post-war settlement in return for their support.
Allied forces land at Cape Helles on the Gallipoli peninsula to support naval attempts at forcing the Dardanelles.
Scottish physiologist John Scott Haldane invents the veil respirator, the first British gas mask.
The first large-scale use of poison gas by the Germans fails to end the stalemate on the Western Front.
British-Indian troops stop the Ottomans re-capturing Basra in Mesopotamia (now Iraq).
The introduction of the Thomas splint, named after the Welsh surgeon Hugh Owen Thomas, drastically cuts the numbers of British soldiers dying from broken femurs.
After initial success, a British-Indian offensive is halted by the Germans at Neuve Chapelle.
The British and French navies unsuccessfully attempt to force the Ottoman-controlled Dardanelles Strait.
The Second Battle of the Masurian Lakes, in East Prussia, ends in a Russian defeat to the Germans.
Germany begins submarine warfare against merchant vessels.
The Royal Engineers form Tunnelling Companies to oversee underground warfare.
The Ottomans fail to capture the Suez Canal, a British-controlled shipping route linking the Mediterranean to the Red Sea.
The Royal Navy is victorious against the Germans at the Battle of Dogger Bank in the North Sea.
The first Zeppelin (airship) raid on Britain sees King’s Lynn and Great Yarmouth bombed by the Germans.
The 3-inch Stokes Mortar is invented and soon becomes the standard British Army mortar of the war.
A Boer rebellion, led by General Manie Maritz against South Africa’s support for Britain and its invasion of German South-West Africa, is eventually suppressed.