My bold … Japan fought on our side in WW1 against the Germans & Austro Hungarians, mainly in the Pacific region where they invaded most of the German possessions there. Later there were naval involvements in the Indian Ocean and even some in the Mediterranean!
Japan during World War I - Wikipedia
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"On 18 December 1916 the British Admiralty again requested naval assistance from Japan. Two of the four cruisers of the First Special Squadron at Singapore were sent to Cape Town, South Africa, and four destroyers were sent to the Mediterranean for basing out of Malta. Rear-Admiral Sato Kozo on the cruiser Akashi and 10th and 11th destroyer units (eight destroyers) arrived in Malta on 13 April 1917 via Colombo and Port Said. Eventually this Second Special Squadron totalled during the war 3 cruisers (Akashi, Izumo, Nisshin), 14 destroyers (8 Kaba-class, 4 Momo-class, 2 ex-British Acorn-class), 2 sloops, 1 tender (Kanto).
The Second Special Squadron carried out escort duties for troop transports and anti-submarine operations. No ship was lost, but on 11 June 1917 a Kaba-class destroyer (Sakaki) was hit by a torpedo from an Austro-Hungarian submarine (U 27) off Crete; 59 Japanese sailors died. The Japanese squadron made a total of 348 escort sorties from Malta, escorting 788 ships containing around 700,000 soldiers, thus contributing greatly to the war effort. A further 7,075 people were rescued from damaged and sinking ships. In return for this assistance, Great Britain recognized Japan's territorial gains in Shantung and in the Pacific islands north of the equator.
With the American entry into World War I on 6 April 1917, the United States and Japan found themselves on the same side, despite their increasingly acrimonious relations over China and competition for influence in the Pacific. This led to the Lansing–Ishii Agreement of 2 November 1917 to help reduce tensions.
In late 1917, Japan exported 12 Arabe-class destroyers, based on Kaba-class design, to France."
I agree WW2 was a totally different scenario and I too have met & talked to men who fought against them & some who had the misfortune to be prisoners of them. To a man they hated and would not forgive the Japanese for the bestial and inhumane way they treated their prisoners. I particularly remember one chap who fought them in Burma telling me of the way his battalion together with a squadron of flame throwing tanks, towards the end of the war, having to clear an Island of what was believed to be several thousand Japanese. Not ONE prisoner was taken after they had seen first hand the treatment our prisoners had suffered after being captured.
I was fortunate enough to have met whilst on business in the USA, a manager of a Mid Western Company I was dealing with who had been in the USMC in the Pacific, who also had similar experiences & still hated the Japs!