The Battle of Imphal (Meitei: Japan Laan, lit. 'Japanese invasion') took place in the region around the city of Imphal, the capital of the state of Manipur in Northeast India from March until July 1944. Japanese armies attempted to destroy the Allied forces at Imphal and invade India, but were driven back into Burma with heavy losses. Together with the simultaneous Battle of Kohima on the road by which the encircled Allied forces at Imphal were relieved, the battle was the turning point of the Burma campaign, part of the South-East Asian theatre of World War II. The Japanese defeat at Kohima and Imphal was the largest up until that time, with many of the Japanese deaths resulting from starvation, disease and exhaustion suffered during their retreat. According to voting in a contest run by the British National Army Museum, the battles of Imphal and Kohima were jointly bestowed as Britain's Greatest Battle in 2013.

In March 1943, the Japanese command in Burma had been reorganised. A new headquarters, Burma Area Army, was created under Lieutenant-General Masakazu Kawabe. One of its subordinate formations, responsible for the central part of the front facing Imphal and Assam, was the Fifteenth Army. Lieutenant-General Renya Mutaguchi was appointed to command this army in March 1943. From the moment he took command, Mutaguchi forcefully advocated an invasion of India. His motives for doing so are uncertain. He had played a major part in several Japanese victories, ever since the Marco Polo Bridge incident in 1937, and believed it was his destiny to win the decisive battle of the war for Japan. He may also have been goaded by the first Chindit expedition, a raid behind Japanese lines launched by the British under Orde Wingate early in 1943. The Allies had widely publicised the successful aspects of Wingate's expedition while concealing their losses to disease and exhaustion, possibly leading Mutaguchi and some of his staff to underestimate the difficulties they would later face.

At the start of 1944, the war was going against the Japanese on several fronts. They were being driven back in the central and southwest Pacific, and their merchant ships were under attack by Allied submarines and aircraft. In Southeast Asia, they had held their lines over the preceding year, but the Allies were preparing several offensives from India and the Chinese province of Yunnan into Burma. In particular, the town of Imphal in Manipur on the frontier with Burma was built up to be a substantial Allied logistic base, with airfields, encampments and supply dumps. Imphal was linked to an even larger base at Dimapur in the Brahmaputra River valley by a road which wound for 100 miles (160 km) through the steep and forested Naga Hills.

Mutaguchi intended to exploit his planned capture of Imphal by advancing to the Brahmaputra Valley. This would cut the Allied lines of communication to the front in northern Burma, where the American-led Northern Combat Area Command was attempting to construct the Ledo Road to link India and China by land, and to the airfields supplying the Nationalist Chinese under Chiang Kai-shek via an airlift over "The Hump" (the Himalaya Mountains). Although the staffs at Burma Area Army and at Southern Expeditionary Army Group (the supreme command for the Japanese forces in southeast Asia and the southern Pacific) had reservations over the scale of Mutaguchi's proposed operation, they were eventually won over by his persistent advocacy. Finally, Prime Minister Hideki Tojo and Imperial General Headquarters gave their approval to the plan.

Mutaguchi intended to block the supply lines to the Allied units in their forward positions, to isolate and destroy them, drawing the Allied reserves into the battle and then capture Imphal. His plan was named U-Go, or Operation C. In detail:

At the insistence of Subhas Chandra Bose, leader of the Azad Hind (a movement which sought to overthrow British rule in India by force, with Japanese assistance), the Indian National Army made a substantial contribution. Originally, the Japanese intended using them only for reconnaissance and propaganda.

All of Mutaguchi's divisional commanders disagreed with the plan to some extent. Sato distrusted Mutaguchi's motives, and Yanagida openly derided his abrasive superior as a "blockhead." Yamauchi was already very ill and fatalistic. Their main reservations concerned supply. Mutaguchi had assumed that success would be achieved within three weeks, but adequate supplies after that period could be obtained only if the Japanese captured Allied supply dumps, as the monsoon rains, which usually descended from about the middle of May, would make the supply routes from the Chindwin almost impossible to traverse. Gambles such as Mutaguchi was making had worked in the past, but could no longer be relied upon, given nearly total Allied air superiority in the area and the improvement in morale and training of British and Indian troops. Mutaguchi proposed to use "Genghis Khan" rations, driving herds of buffalo and cattle rounded up throughout northern Burma across the Chindwin as meat rations on the hoof. However, most of these beasts died from lack of forage and their meat rotted many miles from the troops they were intended to supply.

There were other weaknesses in the plan, which were revealed as the campaign progressed. The Japanese assumed that the British would be unable to use tanks on the steep jungle-covered hills around Imphal. For ease of movement and supply, the Japanese left behind most of their field artillery, their chief anti-tank weapon. As a result, their troops would have little protection against tanks.