When World War I broke out in the golden Summer of 1914, nobody expected that the hosilities would go on for more than six months at the most. Unfortunately for the troops on both sides, the promise that it would all be over by Christmas was rendered hollow as many of them saw out the year in frozen trenches just yards away from the enemy. Thousands of men had already died and it didn't look like the fighting was going to end anytime soon.
1915 began largely as 1914 had ended. The Western Front saw the continuation of costly and hardly-beneficial offensives as tactically bankrupt commanders struggled to adapt to the limitations of trench warfare. New ideas and inventions were utilised in an effort to break the deadlock. Aircraft began to come into their own as a weapon of war whilst chemical weapons were used for the first time as the Germans deployed poison gas on both the Western and Eastern Fronts. The fighting in the east had retained some degree of mobile warfare, with the Germans and Austro-Hungarians gaining the initiative and forcing the Russians out of Galicia and Poland.
This year of the war also saw more nations join the fighting, expanding the two warring factions and earning them the nicknames that would stick for the rest of the war and beyond. The British/French/Russian led coalition became known as the Allies while Germany, Austria-Hungary and the Ottoman Empire became the Central Powers. The Allies, bolstered by Italy's defection, hoped to extend the conflict to other areas around Europe in order to grind down enemy resources and avoid the deadlock of the Western Front, opening up new fronts in Ottoman Turkey and the Italian/Austrian Alps. These new ventures, however, would turn out to be just as frustrating.
January 2nd 1915
- Russia launches an offensive against the Austro-Hungarians in the Carpathian mountains. It will continue until April 12th.
January 19th 1915
- The first air raid on Britain by Zeppelin airships takes place. Two Zeppelins, blown off-course by strong winds, drop bombs on several coastal towns in Norfolk, killing four people.
January 24th 1915
- Elements of the British Grand Fleet and the German High Seas Fleet face off at the Battle of Dogger Bank in the North Sea. As the German battlecruiser SMS Blücher is sunk with the loss of most of her crew, the encounter is considered a victory for the British.
January 28th 1915
- The Ottomans attack from Palestine into British-controlled Egypt, hoping to capture the Suez Canal and deprive the British of the quickest route to India. The attack fails and the Ottomans withdraw by February 3rd.
January 31st 1915
- The Germans use poison gas for the first time, deploying chlorine gas against the Russians at the Battle of Bolimov.
February 4th 1915
- Germany begins a campaign of unrestricted submarine warfare against Allied and neutral merchant shipping, intending to starve Britain out of the war and deprive the Allies of American war material.
February 7th - 22nd 1915
- The Russian Tenth Army is defeated by the Germans at the Second Battle of the Masurian Lakes. The Russian position in Poland is left greatly weakened as a result.
February 19th 1915
- The Allies launch the Dardanelles campaign against the Ottoman Empire. British and French ships bombard the Ottoman defenses around the Dardanelles Straits in preparation for a land assault which is hoped will capture the Ottoman capital, Constantinople, and reopen access to the Black Sea.
March 10th - 13th 1915
- On the Western Front, a British attempt to take the offensive at the Battle of Neuve Chapelle is halted.
March 22nd 1915
- The siege of Przemyśl ends with the Russians capturing the Galician fortress city from the Austro-Hungarians.
April 22nd 1915
- The Germans in Flanders launch the Second Battle of Ypres. The German assault begins with a chlorine gas attack on the Moroccan and Algerian colonial troops of the French 45th and 78th Divisions at Gravenstafel. The gas kills over 6000 men in less than ten minutes and opens a four-mile wide gap in the Allied line as the survivors flee. A lack of reinforcements and concerns about what the lingering gas might do to their own troops prevent the Germans from fully exploiting this success and the gap is quickly refilled by Canadian troops.
April 24th 1915
- The fighting at Ypres continues with a second German gas attack on the Canadian frontline near the village of St Julien. Improvised countermeasures against the gas fail and the Allied line cracks once again, allowing the Germans to capture St Julien and much of the northern sector of the Ypres salient. The Allies pull back and hastily reform their frontline much closer to Ypres itself.
April 25th 1915
- Italy secretly signs the London Pact, thereby agreeing to join the Allies.
- The first Allied forces land on the Gallipoli peninsula in Turkey, beginning the land phase of the Dardanelles campaign. It turns out that the naval bombardment was not as effective as had been hoped and the disembarking British, French, Australian and New Zealand troops immediately encounter stiff Ottoman resistance.
April 28th 1915
- An Allied offensive at Gallipoli, the First Battle of Krithia, is repelled by the Ottomans.
May 1st - 3rd 1915
- August von Mackensen's German forces break through the Russian lines at the Battle of Gorlice-Tarnów, paving the way for a reconquest of Galicia by the Central Powers.
May 6th - 8th 1915
- The Second Battle of Krithia at Gallipoli produces exactly the same outcome as the first.
May 7th 1915
- The British ocean liner RMS Lusitania is sunk off the coast of Ireland by the German submarine U-20. Among the 1198 dead are 128 American citizens. The sinking triggers outrage in the United States despite the German embassy having warned in advance that passengers sailing under British colours in British waters do so at their own risk.
May 12th 1915
- Troops from South Africa capture Windhoek, the capital of German South West Africa.
May 23rd 1915
- Italy declares war on Austria-Hungary.
May 25th 1915
- The Second Battle of Ypres draws to a close. The Germans have not broken through but they have managed to considerably reduce the size of the Ypres salient. Ypres itself is now well within range of German artillery and the old town, having already suffered considerable damage, is gradually shelled to destruction over the remainder of the war.
June 4th 1915
- The Ottomans repel another Allied offensive at the Third Battle of Krithia.
- The Russians abandon Przemyśl as their positions in Galicia continue to collapse.
June 23rd 1915
- The Italian Front sees its first action of the war as the Italians launch the first of a series of offensives against the Austro-Hungarians along the River Isonzo, which straddles the border between the two countries. The First Battle of the Isonzo rumbles on indecisively until July 7th.
June 27th 1915
- The Germans and Austro-Hungarians recapture the Galician provincial captial, Lemberg from the Russians.
July 9th 1915
- The remaining German forces in South West Africa surrender to the South Africans.
July 18th 1915
- Italy launches the Second Battle of the Isonzo. The attack ends on August 3rd.
August 5th 1915
- German forces advancing in Poland capture Warsaw from the Russians.
August 6th - 29th 1915
- The British in Gallipoli launch the August Offensive, also known as the Battle of Sari Bair. This is the final attempt to dislodge the Ottomans from the peninsula and ends in failure.
September 1st 1915
- Germany suspends its policy of unrestricted submarine warfare in response to the American outcry that followed the sinking of the Lusitania.
September 8th 1915
- Tsar Nicholas II of Russia removes Grand Duke Nicholas as Commander-in-Chief and assumes personal command of the Russian armed forces.
September 19th 1915
- German forces advancing eastwards from East Prussia capture the Russian city of Vilnius.
September 25th - 28th 1915
- A major British offensive on the Western Front, the Battle of Loos, ends in failure.
October 6th 1915
- Bulgaria joins the Central Powers.
- Austria-Hungary and Bulgaria, backed up by substantial German forces, launch a major invasion of Serbia.
October 11th 1915
- The prospect of abandoning the Dardanelles campaign and evacuating the Allied forces from Gallipoli is raised for the first time. The British commander in Gallipoli, Sir Ian Hamilton, resists the proposal and is subsequently replaced by Sir Charles Monro. The decision to evacuate is made later in the month.
October 14th 1915
- Bulgaria declares war on Serbia.
October 15th 1915
- The United Kingdom declares war on Bulgaria.
October 16th 1915
- France declares war on Bulgaria.
October 18th 1915
- Italy launches the Third Battle of the Isonzo. The attack ends on November 4th.
October 19th 1915
- Italy and Russia declare war on Bulgaria.
October 27th 1915
- A French army lands at the Greek port of Salonika. Together with British and Italian support, it sets up a stationary Balkan Front to protect neutral Greece from the German, Austro-Hungarian and Bulgarian forces advancing south through Serbia.
November 10th 1915
- Italy launches the Fourth Battle of the Isonzo. The attack ends on December 2nd.
November 15th 1915
- Winston Churchill, having already lost his position as First Lord of the Admiralty over his role in the Gallipoli fiasco, resigns from Britain's coalition government and goes off to fight on the Western Front, commanding the 6th Battalion of the Royal Scots Fusiliers in Belgium.
November 22nd - 25th 1915
- A British-Indian force campaigning in the Ottoman province of Mesopotamia (modern day Iraq) is repulsed by the Ottomans at the Battle of Ctestiphon. The British commander, Major-General Charles Townshend, orders a retreat to the south.
November 27th 1915
- The Serbian army collapses in the face of the Central Powers' invasion. Many Serbian troops head southwest through neighbouring Albania and are evacuated from the Adriatic coast by Allied ships.
December 7th 1915
- Charles Townshend's 8000-strong British-Indian army, along with the reinforcements sent by the British from Basra, is besiged by the Ottomans at the town of Kut-al-Amara, 100 miles south of Baghdad.
December 19th 1915
- Douglas Haig replaces Sir John French as commander of the British and Commonwealth forces on the Western Front.
December 20th 1915
- The last Allied troops leave the Sulva and ANZAC beachheads at Gallipoli, completing the first phase of the Allied evacuation that had been decided upon in October. British troops remain stationed at Cape Helles on the tip of the Gallipoli peninsula.