Czar Nicholas II inspects his troops during the partial mobilisation in July 1914. On 25 July, the Russian Council of Ministers agreed on measures for a partial mobilisation of four military districts adjacent to Austria-Hungary, as well as the Russian Navy, which would come into force on 26 July.

On 25 July 1914, Emperor Franz Joseph issued a mobilisation order for the 1st, 2nd, 3rd, 4th, 5th, 6th, 7th, and 8th field armies, with operations to commence against Serbia on the 28th. It came after Vienna received what it believed to be an unsatisfactory reply to its ultimatum of the 23rd.

Hawker Hurricane Mk I P3166 VY-Q, flown by the CO of No. 85 Squadron, Squadron Leader Peter Townsend, taxiing out at Castle Camps on 25 July 1940, during the Battle of Britain. Castle Camps served as a satellite station for RAF Debden and later in the war, RAF North Weald. 📸 IWM (HU 104488)

24 July 1914: The Belgian Minister for Foreign Affairs, Julien Davignon, sent a telegram to Belgium's ambassadors stating that, as a Franco-German war was becoming increasingly likely, orders were soon to be issued for the mobilisation of the Belgian Army to safeguard Belgium's neutrality.

24 July 1914: Expecting an Austria-Hungary declaration of war against them soon, Serbia mobilised its army while Austria-Hungary broke off diplomatic relations. The British Ambassador to Austria-Hungary reported to London: "War is thought imminent. Wildest enthusiasm prevails in Vienna."

24 July 1914: France began withdrawing troops from Morocco and began preliminary steps for full mobilisation. The French navy had already started to fully concentrate at Toulon. This followed an agreement with Britain that the Royal Navy would cover the Channel and protect France's Atlantic coast.

23 July 1914: Germany's military and political leadership returned secretly to Berlin to address the growing crisis in Europe. The military leaders, Moltke and Falkenhayn, advocated for an immediate German response following an Austro-Hungarian attack on Serbia, with an offensive against Russia.

With tensions rising in Europe, a grand review of the Royal Navy was held at Spithead on 17 and 18 July 1914. A test mobilisation of the reserve Third Fleet had begun on 15 July, and the three Home Fleets were at heightened readiness when orders for a full mobilisation came through on 1 August.

King George V climbing the Butte de Warlencourt, Le Sars on 13 July 1917 during a visit to the Western Front. This prominent, chalky ancient burial mound had been a heavily fortified German stronghold. 📸 Lt John Warwick Brooke / IWM (Q 5668)

Russian troops break and run in the face of a German counterattack in a village in East Galicia in July 1917, during the Russian summer offensive. The Russian offensive failed with heavy casualties and led to unrest in Petrograd and contributed to the fall of the Provisional Government in November.

A patrol from 21 Special Air Service (Reserve) Regiment stops to check a compass bearing in a wood in South Jutland during a training exercise against the Danish Home Guard in July 1970. 21 SAS were to form part of NATO stay-behind forces in the event of a Warsaw Pact invasion. 📸 Leslie Wiggs

The British Mark V tank made its combat debut on 4 July 1918 during the Battle of Hamel in northern France, when sixty Mark Vs supported Australian troops in action. The successful combined arms operation saw the capture of the village of Hamel from the Germans that day.

Carl Röchling's painting of Captain August von der Groeben’s Austrian horse artillery battery being overrun by the Prussian Guards during the Battle of Königgrätz on 3 July 1866. Groeben, along with 53 men and 68 horses were killed attempting to hold off the Prussian advance.

Men of 12 Platoon, 'B' Company, 6th Battalion, Royal Scots Fusiliers, advancing into St Manvieu during Operation EPSOM on 26 June 1944. The Royal Scots Fusiliers secured their initial objectives of St Manvieu and La Gaule in close quarters and hand-to-hand fighting.

Portuguese infantry battalion on the march near Locon on 24 June 1917. The Portuguese Expeditionary Corps deployed to France in early 1917. The German Empire had declared war on Portugal in March 1916 after the Portuguese seizure of German merchant ships. 📸 Lt John Warwick Brooke / IWM (Q 5537)

USS ALABAMA and USS SOUTH DAKOTA at speed during combined British and US fleet exercises out from Scapa Flow on 24 June 1943. Photo taken from HMS ANSON by Lt J A Hampton. 📸 IWM (A 17626)

Winston Churchill watching a Landing Craft, Mechanised Mark 1 (LCM 1) containing a Valentine tank being launched down the slipway of Landing Craft Carrier TSS Iris during combined operations training on Loch Fyne in June 1941. 📸 IWM H 11177

22 June 1812: Napoleon issued a formal declaration of war against the Russian Empire, with the French ambassador delivering the diplomatic note in St Petersburg. Two days later, French and Allied forces would cross the Nieman River, marking the start of Napoleon's invasion of Russia.

Soldiers of the 57th Infantry Regiment, 9th Infantry Division, XXXXIV Army Corps of German Army Group South crossing the Soviet border near border marker IV/95 on 22 June 1941, the first day of Operation BARBAROSSA.

21 June 1813: British, Portuguese, and Spanish forces under Sir Arthur Wellesley, Marquess of Wellington, defeated the French, led by Joseph Bonaparte and Marshal Jean-Baptiste Jourdan, at the Battle of Vitoria, in northern Spain during the Peninsular War.

21 June 1919: Rear-Admiral Hans Hermann Ludwig von Reuter ordered the German High Seas Fleet to be scuttled at Scapa Flow to prevent the ships from falling into Allied hands. 74 warships were sunk or beached, and 9 sailors were killed.

Troops of the Norwegian Brigade stage a bayonet charge through a smokescreen during training at Carronbridge, Dumfriesshire, in June 1941. 📸 Walter Thomas Lockeyear / IWM (H 11131)

20 June 1895: The Kaiser Wilhelm Canal (Kiel Canal) linking the North Sea at Brunsbüttel to the Baltic Sea at Kiel-Holtenau was opened. It allowed the German navy to move from the Baltic to the North Sea, bypassing the Danish Straits. From 1907 to 1914, it was widened for Dreadnought-sized warships.

Prince Chun of China during a visit to the Imperial German Army manoeuvres of 1901. Following the German suppression of the Boxer Rebellion in Peking, the Prince came to Germany to formally apologise to the Kaiser for the murder of the German Minister von Ketteler in Peking on 20 June 1900.

On 18-19 June, French Marshal Grouchy fought the Battle of Wavre against Prussian forces under General Johann von Thielmann. Though the French secured a tactical victory, after learning of the defeat at Waterloo, Grouchy executed a rapid retreat southward to Namur to evade advancing Allied troops.

Jan Hoynk van Papendrecht's painting depicting the first meeting of Dutch and Prussian troops near Maison du Roi on the evening of 18 June 1815, after the Battle of Waterloo.

Major-General Sir John Campbell (seated) and his aide-de-camp Captain Gustavus Hume photographed by Roger Fenton during the Crimean campaign. Shortly after the photo was taken, Major-General Campbell was killed in the attack on the Great Redan on 18 June 1855 during the Siege of Sevastopol.

18 June 1815: The Prussian III Corps under the command of General Johann von Thielmann engaged three corps of the French army under the command of Marshal Grouchy at Wavre. This action prevented Grouchy from linking up with Napoleon at Waterloo.

Richard Simkin's painting depicting the rearguard action by the 1st Life Guards of Major-General Lord Somerset's Household Brigade at Genappe on 17 June 1815, charging the pursuing French cavalry while covering the retreat of the Duke of Wellington's Anglo-Allied army from Quatre Bras.

In Britain's worst maritime disaster, RMS Lancastria was sunk on 17 June 1940 by a German air attack off the port of Saint-Nazaire during Operation AERIAL with over 4,000 fatalities. Prime Minister Winston Churchill ordered that news of the sinking be kept secret from the British public.