Résumé of main events of 1915.
| 1 January | HMS Formidable is sunk in the English Channel by German submarine SM U-24; nearly 600 lives lost. | ||||
| 1 January–4 February | Third thrust for Warsaw; Russians hold up enemy on the Bzura-Ravka Rivers; Russian successes in Transcaucasia. | ||||
| 1 January–17 April | Russo-Austrian struggle in Galicia and the Carpathians; Russians eventually successful. | ||||
| 2 January | ▶ Russian successes on the Bzura and advance in the Bukovina. | ▶ Turkish transport Perk-I-Skefket mined and sunk in Bosphorus. | |||
| 3 January | Turks take and lose Tabriz to the Russians; enemy activity (v. Egypt) in Syria. | ||||
| 14 January–July | Campaign in German South West Africa. | ||||
| 24 January | Battle of the Dogger Bank. | ||||
| 3 February | 12,000 Turks attack Suez Canal and are beaten off. | ||||
| 3 February–21 March | Russians, driven from East Prussia, hold up Germans on the Niemen, Bobr and Narev rivers. | ||||
| 18 February | German submarine blockade of Great Britain begins. | ||||
| 19 February–6 April | British naval attacks on the Dardanelles (entrance cleared 26 February; big attack on Narrows fails, 18 August). | ||||
| March | Fighting (British v. Turks) in Lower Mesopotamia. | ||||
| 8 March–15 March | Battle of Neuve Chapelle. | ||||
| 22 March | Przemyśl surrenders to the Russians. | ||||
| 9 April | British and French military force (120,000 under Generals Sir I. Hamilton and d’Amade) concentrate outside Dardanelles. | ||||
| April – July | Appalling Armenian massacres (?800,000) by Turkish order. | ||||
| 22 April–24 May | Second battle of Ypres. (British pressed back.) | ||||
| 25 April–28 April | Battle of the landings in Gallipoli (S.W. corner and Anzac Cove). | ||||
| 28 April–3 July | Great Austro-German attack in Galicia; | ▶ Russians are driven back from the Dunajec to the San, 28 April–12 May; | ▶ From the San to Lemberg, 15 May–20 June; | ▶ Fall of Przemyśl, 3 June; of Lemberg, 22 June; | ▶ Germans held on the Zlota Lipa, 28 June–3 July. |
| 7 May | RMS Lusitania is torpedoed. | ||||
| 15 May–25 May | Battle of Festubert. | ||||
| May to July | Heavy and intermittent fighting in Gallipoli. | ||||
| June | British take offensive East of the Suez Canal. | ||||
| 26 June–4 July | Battle of the Argonne. | ||||
| 2–18 July | Pressure on the Warsaw salient from the north-west and south-west (the fall of Przasnysz, 15 July). | ||||
| 9 July | Surrender of the Germans in south-west Africa. | ||||
| 14 July | National Registration Bill is passed. | ||||
| 15 July–30 September | Russian retreat from Warsaw; | ▶ Fall of Ivangorod 4 August, of Warsaw 5 August, of Kovna 17 August, of Novo Georgievsk 19 August, of Osovyets 23 August; | ▶ Battle of Meiszagola-Vilna 2–12 September; | ▶ Fall of Prinsk 16 September, of Vilna 18 September; | ▶ Germans checked, and Russian counterstrokes in Volhynia and Galicia 18–30 September. |
| 17 July | ▶ Secret treat between Bulgaria and the Central Powers; | ▶ Defeat of Allied diplomacy. | |||
| 6–10 August | Landing and battle of Suvla Bay, etc. | ||||
| 10–21 August | Naval fighting in the Baltic and Gulf of Riga; Germans are repulsed. | ||||
| 7–29 September | British occupy Bushire (Persia). |