entered the First World War on the side of Britain
, by declaring war on Germany
about four weeks after the assassination of Archduke Ferdinand
It was the first time in history that Japan went to war allied to another nation. Japan was motivated to capture nearby German possessions, including Tsingtao in China, several islands in Micronesia and the South Pacific, and parts of New Guinea. Japan signed a defence treaty with Britain in 1902 although it did not compel either party to assist the other in the event of hostilities. Winston Churchill as First Lord of the admiralty knew that Britain would depend on Japan to protect Britain's interests in East Asia, allowing the Royal Navy to be closer to the action in Europe. Sir Edward Gray, Britain's Foreign Secretary was conversely quite hawkish and suspicious of Japan's motives, particuarly in Manchuria. Japan was an emerging Pacific power, having defeated the Russians ten years earlier. With 16 battleships and 55 destroyers Japan's navy was the world's fourth largest. It also boasted 300,000 men under arms out of a population of 55 million.
Internally, Japan was divided over supporting the allies over the Central Powers. The Japanese navy had received support and training from Britain, while the army modelled themselves on the Prussian army, and so their sympathies were mixed. The Japanese Cabinet included representatives from both arms of service, and so there were divisions over the extent of co-operation Japan would lend to the British. There was the feeling that in international fora and in trade negotiations Japan was not being taken seriously given its naval strength and contributions.
Japanese Prime Minister Prince Yamagata Aritomo delivered an ultimatum on 15 August 1914 to Germany, demanding the Germans surrender their colonial port of Kiaochow in China and their Pacific possessions, and to scuttle or surrender their fleet. The Germans did not respond, and so the Japanese declared war on 23 August 1914.
Even before Japan declared war, she sent naval vessels to intercept the German Pacific Squadron fleet under the command of Admiral von Spee around Tsingtao Harbour, which was escaping from Kiaochow. The blockade lasted around a month and involved a few skirmishes, including the world's first air raid by carrier borne aircraft when seaplanes from the Japanese tender Wakamika sunk a German minelayer.
Japanese troops landed near Lungkao on the Shantung Peninsula on 2nd September, and advanced southwards. They beseiged Kiaochow, defended by a garrison of 5,500 German and Austro-Hungarian troops. On September 24th a British expiditionary regiment consisting of Sikh and Welsh troops came to join up with the Japanese soldiers (their presence somewhat unwanted by the Japanese in what was perceived as their backyard). Kiaochow was eventually taken on 7 November 1914.
In the Pacific...
At around the same time, Japanese forces landed on Palau, the Marianas, the Marshalls, Yap Island, the Carolines and the German port of Rabaul on New Britain, while Australian forces captured New Guinea and New Zealand just managed to snatch Samoa away in time. In late 1914 a tentative agreement was made between Britain and Japan that roughly stated that Commonwealth forces would not claim islands north of the Equator in the Pacific.
Japan's navy performed many tasks in the Asia Pacific region during the First World War on behalf of the Allies. It escorted ANZAC troops sailing from Australia to Aden, keeping an eye out for German raiders that operated in the Indian Ocean. Vessels patrolled areas as far afield as South Africa and Mexico, while keeping an eye closer to home as some German shipping had snuck into the neutral Philippines. Japanese marines were used in February 1916 to quell a mutiny by Indian troops in Singapore.
An interesting and overlooked aspect of World War One was Japan's naval contribution in the Mediterranean Sea. By 1917 Britain was hemmoraging money and men after years fighting in Europe, and desperately needed more military resources. Its merchant shipping was being mercilessly mauled at sea by U-boats. In exchange for British recognition of Japanese claims in China and the Pacific, Japan initially sent the cruiser Akashi and eight destroyers to Malta (this number rose to seventeen, alongside British vessels commanded by a Japanese crew). The fleet protected allied shipping convoys in the Mediterranian, and sent troops from Egypt to Salonika and Marseilles as part of the 1918 offensive. In one famous incident the destroyer Matsu saved over three thousand crew from the torpedoed transport Transalyvania off the French coast. In all, the Japanese escorted 788 ships in the Mediterranean, including transports carrying 700,000 British Commonwealth troops.
Japan came out of the war with a fistful of minor colonies with tenuous international recognition, at the comparatively low cost of 2,000 dead. Japan would later choose not relinquish them when finally the League of Nations sought that they be placed in trusteeship. One significant outcome from the war was that Japan was able to gear its industrial base for war production, while profitably building ships for the British and American navies.
Interestingly, many Japanese were not aware that their country was contributing so much of its forces, or even that Japan was at war. One negative outcome of the prosperity created by the ship building boom was an inflationary explosion in wages and prices, causing rice riots in major cities.
Japanese soldiers duly took their place in the international victory parade in Paris on 14th July 1919. While the allies were grateful with Japan's conduct and contributions in the war, and even in awe of their discipline and efficiency, their successes had made the European allies even more wary about where Japan's imperial ambitions lay.