After the Great War broke out, Japan's naval and military assistance was an important concern for the British government. Arthur Balfour was the only politician involved in this matter from the beginning to the end of the war. Until he became Foreign Secretary he had little expectation of Japan's assistance. However, the difficult circumstances of the war forced him to review his opinion about the value of Japan's help, as Britain was suffering badly from a shortage of manpower and munitions. As Foreign Secretary he had high hopes of Japan's assistance and did not hesitate to launch negotiations to secure her aid.<br>Balfour sought Japan's naval assistance and eventually succeeded in inducing her to despatch her destroyers to the Mediterranean. The price for this, namely guaranteeing Japanese rights in Shantung and the Pacific islands, was regarded as a permissible concession. The Japanese government, however, expressed disapproval at his request that they sell battle-cruisers to Britain. Balfour promptly put forward a new proposal to borrow the battlecruisers instead, based on his assumption that lending them would be more agreeable to Japan than selling them. He could not conceal his disappointment and dissatisfaction with the Japanese government's refusal to fulfil this modified request. He was not convinced by the reasons the Japanese government presented and criticised Japan's reluctance to help Britain.<br>In seeking Japan's military assistance, Balfour faced two obstacles. One was the difficulty of transporting Japanese troops to the European field. Many troopships would be needed to carry a large number of Japanese soldiers to the western or Salonica front. Britain and the Allied Powers, however, could not afford to allocate so many ships as they had a severe deficit of tonnage. The other obstacle was the need to harmonise the Japanese military campaign with the political interests of Britain and the Allied Powers. Russia did not want to receive Japanese soldiers on the eastern front due to her fear of massive territorial concessions to Japan. Although Balfour considered that Mesopotamia was the most promising theatre from which to deploy Japanese troops, he was obliged to renounce this idea due to strong opposition from the India Office and the Government of India. He continued to seek a location where transportation difficulties could be overcome and which was compatible with the interests of the other powers, and saw Siberia as the most favourable field. Henceforth Japan's military assistance was regarded as the Siberian Intervention, and Balfour continued to tackle this subject.