31 January 1917
Germany announces the resumption of unrestricted submarine warfare, hoping to starve Britain into submission.
3 February 1917
The United States severs diplomatic relations with Germany as U-Boats threaten US shipping. Interception of the Zimmerman Telegram reveals that Germany is attempting to form an alliance with Mexico should the US join the war on the side of the Entente Powers.
13 February 1917
Mata Hari is arrested in Paris as a German spy.
21 February 1917
The Great German Withdrawal begins. They will evacuate Serre, Miraumont, Petit Miraumont, Pys and Warlencourt, falling back 25 miles to establish stronger positions along the Hindenburg Line.
24 February 1917
Turkish retreat to Baghdad, abandoning Kut in Mesopotamia.
11 March 1917
Baghdad is taken by the British after three days fighting. They go on to take much of Mesopotamia.
15 March 1917
Tsar Nicholas II abdicates and a provisional government is appointed. Demise of the Russian Army frees German troops for the Western Front.
26 March 1917
The First Battle of Gaza, Palestine, as the British attempt to cut off the Turkish forces in Mesopotamia from their homeland. They fail to take the town and are forced to withdraw.
6 April 1917
US declares war on Germany. Troops begin to mobilise immediately.
9 April 1917
16 April 1917
The Second Battle of Aisne begins. The appalling losses trigger mutinies within the French Army.
19 April 1917
The Second Battle of Gaza begins in Palestine – a loss of 6,000.
7 June 1917
13 June 1917
Germans launch the first major heavy bombing raid over London. Bombs dropped from 18 Gotha GV aircraft kill 162 people and injure 432.
25 June 1917
First American troops arrive in France.
16 July 1917
T E Lawrence and the Arabs liberate Aqaba in Jordan after crossing the Nefu desert. This opens the route north for the Arab Army and isolates the Turkish Army in Mesopotamia.
31 July 1917
The Third Battle of Ypres (also known as the Battle of Passchendaele) begins along a 15 mile front in Flanders. Initial attacks are successful as the German forward trenches are only lightly manned.
15 August 1917
The Battle of Lens (Hill 70). Canadian troops are in the vanguard of this assault. Hill 70 is only 15 feet higher than the surrounding landscape but it dominates the battlefield. The Canadians take the hill and hold it against five German counter attacks. Allies lose 9,200 men.
9-10 September 1917
9 October 1917
Battle of Poelcapelle (part of the final phases of the Third Battle of Ypres). 25mm of rain falls in the next 48 hours on already saturated ground. The previous bombardments smashed the drainage systems and the battlefield turns into a quagmire.
12 October 1917
The British launch their latest assaults at Ypres against the Passchendaele Ridge. New Zealand and Australian divisions in the vanguard of the attack take terrible casualties, then are bogged down in the mud and are forced back to their start lines.
19 October 1917
The last airship raid on Britain is carried out by 11 Zeppelins.
26 October 1917
The Second Battle of Passchendaele begins with 20,000 men of the Third and Fourth Canadian Divisions. It cost the Allies 12,000 casualties for a gain of a few hundred yards.
30 October 1917
Reinforced with the addition of two British divisions, a second offensive is launched in torrential rains to capture Passchendaele.
The Allies hold the town for the next five days in the face of repeated German shelling and counter-attacks.
31 October 1917
7 November 1917
October Revolution in Russia led by Lenin
British capture Gaza.
10 November 1917
Battle of Passchendaele ends. After months of fighting, the Allies have advanced only 5 miles, but have taken the high ground’. Half a million men are casualties, of which around 140,000 have been killed.
20 November 1917
The Battle of Cambrai begins. During the attack, Royal Flying Corps aircraft drop bombs on German anti-tank guns and strong points to clear a path for the Allied tanks and ground troops. It is an early example of the ‘Blitzkrieg’ tactics destined to be used by the Germans so effectively in World War Two.
11 December 1917
Britain liberates Jerusalem, ending 673 years of Ottoman rule.