8 February - Japanese torpedo boats launched a surprise attack on the Russian fleet at anchor in the harbour of Port Arthur, causing severe damage. At the same time, the main Japanese battle fleet of Vice-Admiral Heihachiro Togo appeared off the port to engage the Russian shore batteries at long range. Togo also instituted a blockade of Port Arthur.
9 February - The Japanese armoured cruiser squadron under Vice-Admiral Hikonojo Kamimura, while escorting the transports of an expeditionary force, entered the harbour of Chemulpo (modern-day Inchon, Korea) and attacked two Russian cruisers there. One of the ships was sunk, while the other was so severely damaged that it was eventually sucttled by its crew.
10 February - The Japanese government issued a declaration of war to the Russian government.
17 February - The Japanese First Army, under General Tamesada Kuroki, began troop disembarkation at Chemulpo, followed by an advance through Korea to the Yalu River, to cover military operations taking place at Port Arthur.
8 March - 13 April - Russian Admiral Stepan Makarov arrived from Russia to take command of the Russian fleet on 8 March. Upon arrival, he began a series of sorties to harass the blockading Japanese cruisers, while avoiding Togo's main battle fleet. Returning from one of these sorties, Makarov's flagship, Petropavlovsk, struck a Japanese mine and sank will all abroad on 13 April. After that, the Russian fleet remained passively in port. The loss of this charistmatic Admiral was a catastrophe for the Russian navy.
April - May - Russian General Alexei Kuropatkin, who was also the Minister of War, assumed command of all Russian field forces in the east. Recognising Russia's unpreparedness for war, Kuropatkin knew that the Japanese would try to achieve an early victory to knock Russia out of the war. On 3 May, he began concentrating all his forces in 3 main groups south of Mukden - 35,000 men under General Stakelberg in the Haicheng-Kaiping area north of Port Arthur; 30,000 men under General Keller to guard the passes west of the Yalu River; 7,000 men under General Zasulich to cover the Yalu crossings; and 40,000 men under Kuropatkin himself in reserve at Liaoyang.
An additional force of 40,000 men under General Anatoli M. Stesel guarded the fortress of Port Arthur. Recognising the initial Japanese numerical advantage, Kuropatkin planned to let the Japanese temporarily besiege Port Arthur, which he was confident could hold out for several months. Then he would fall back slowly towards Harbin, delaying the Japanese advance into Manchuria until reinforcements arrived from other parts of Russia. Kuropatkin expected that the Trans-Siberian Railway would be able to transport 40,000 men per month to the Far East. By the end of summer, Kuropatkin felt that he would then have sufficient forces to return southward to relieve Port Arthur and drive the Japanese from Manchuria.
Unfortunately for Russia, its Viceroy of the Far East Adimiral Evgeni Alekseev, who was appointed as the Russian generalissimo by Tsar Nicholas II, insisted on an immediate offensive against the Japanese, whom he considered as upstarts. He ordered Kuropatkin to abandon his sound defensive-offensive plan, and to launch an attack instead.
30 April - 1 May - The first major land campaign of the war, the Battle of the Yalu, broke out when General Kuroki's First Japanese Army arrived at the Yalu River near Wiju and was met by General Zasulich's forces. Despite the overwhelming numerial superiority of the Japanese forces, Zasulich chose to confront them instead of pulling back to a more defensible position, resulting in his forces being routed. The Russian side suffered 2,500 casualties, while the Japanese lost 1,100 out of 40,000 men. With this victory, Kuroki's forces were able to advance into Manchuria.
5 - 19 May - The Japanese Second Army under General Yasukata Oku landed on the Liaotung Peninsula at Pitzuwu, about 40 miles northeast of Port Arthur. As his forces moved southwards, they were stopped by a powerful Russian defensive position based on Nanshan Hill, at the narrowest part of the peninsula. Meanwhile, the Japanese Fourth Army under General Michitsura Nozu began disembarking at Takushan, west of the Yalu River. As the Japanese stranglehold tightened around Port Arthur, Admiral Alekseev fled north to Kuropatkin's headquarters at Liaoyang.
The Siege of Port Arthur
25 May - The Battle of Nanshan began when General Oku's troops began a frontal assault on Nanshan Hill, an outpost of Port Arthur garrisoned by 3,000 Russian men. While the initial attack was repulsed, the Japanese started to attack from the flanks, forcing the Russian defenders to flee in haste. The ferocity of the battle was reflected in Oku's 4,500 losses out of 30,000 men. Russia's loss was about 1,500 men.
The capture of Nanshan Hill meant that Port Arthur was now surrounded by Japanese forces both on land and at sea. The Japanese began to strengthen their forces at the port of Dalny (today's Dalian), near Port Arthur. Meanwhile, while Nogi was entrusted with the siege of Port Arthur, Oku's Second Army tunred northward to confront Russian commander Stakelberg's offensive on Alekseev's orders.
1 - 22 June - As Nogi gradually built up his forces at Dalny, the Russian commander in Port Arthur General Stesel merely waited for the attack. The port fortress complex consisted of three main lines: an entrenchment surrounding the old town itself; a ring of concret forts; and a series of fortified hills, though some fortifications were yet to be completed. Excluding the Russian naval personnel, the garrison forces amounted to 40,000 men and 506 guns. While the food supply was insufficient, there was no immediate danger of starvation.
By the end of July, Nogi had built up his forces to 80,000 men with 474 field and siege guns. Nonetheless, it was still premature to attack the fort, given its formidable defences.
26 June - General Stesel attempted an attack which was quickly repulsed by the Japanese.
27 - 28 June - The Japanese began to probe the fort defences by launching some attacks on the outer ring of forts.
7 - 8 August - Convinced that the Russian defences were falling, Nogi ordered an attack on the eastern hills of the outer defence, which were captured after fierce fighting.
10 August - Tsar Nicholas II orderd Admiral Vitgeft to break out and join the Vladivostok squadron. Marking the start of the Naval Battle of the Yellow Sea, Vitgeft led his squadron of 6 battleships, 5 cruisers and 8 destroyers, which was quickly followed by Togo's forces. As Japanese gunnery was more superior to the Russian's, the four Japanese modern battleships fired much more effectively than their Russian counterparts. Both fleets suffered severe damage. After 90 minutes of action, a 12-inch shell struck Vitgeft's flagship, Czarevich, killing the Admiral. This resulted in confusion among the Russian forces, causing the Russian fleet to flee in disorder. In the ensuing chaos, one Russian cruiser was sunk, while several others reached neutral ports where they were interned. Nonetheless, most of the Russian ships managed to return to Port Arthur.
To be continued in Part Two of the chronology