A quiet pocket of British India until then, the remote state of Manipur was the scene of devastating fighting from March to July 1944 when the Japanese advanced westwards from captured Burma, backed by a rebel Indian force.
Tens of thousands of soldiers were killed fighting for the cities of Imphal and Kohima, with the Allied victory a major turning point in the Asia campaign that was voted as Britain's greatest battle by the National Army Museum of London in April last year.
Diplomats from Britain, Australia and the US made speeches on Friday and laid wreaths on the first day of the two-day ceremony in Imphal, capital of Manipur state.
"It was very moving. It's very important to remember the sacrifice thousands of men made," Scott Furssedonn-Wood, British deputy high commissioner for eastern India, told AFP by phone.
"When you stand at a grave of hundreds of men who sacrificed their lives, it helps you relate better to an epic battle that changed world history."
The British and Indian forces, under the command of Lieutenant-General William Slim, drove back the invasion at a cost of 17,500 lives. Japan lost 30,000 men, according to the Commonwealth War Graves Commission.
Many historians feel that the battles in India have been overlooked, partly because the Allied invasion of occupied Europe known as D-Day took place while they were still being fought.
"It's being forgotten. Even I didn't know about the battle until my grandfather told me that he had to attend the service today," said local Kakai Singsit, whose 91-year-old grandfather Mehkhosong fought in Kohima.
"If this memorial didn't happen today, many youths, including myself, would not know about the battle," 29-year-old Singsit told AFP by phone.
Get Breaking news, live coverage, and Latest News from India and around the world on NDTV.com. Catch all the Live TV action on NDTV 24x7 and NDTV India. Like us on Facebook or follow us on Twitter and Instagram for latest news and live news updates.