Short answers, pulled from the story.
The Battle of Imphal was fought from March until July 1944 around Imphal, the capital of Manipur in northeast India. Japanese forces attempted to destroy Allied forces at Imphal and invade India, but were driven back into Burma with heavy losses. Together with the simultaneous Battle of Kohima, it was the turning point of the Burma campaign in World War II.
Lieutenant-General Renya Mutaguchi commanded the Japanese Fifteenth Army and was the principal architect of the offensive, named U-Go or Operation C. His superior, Lieutenant-General Masakazu Kawabe, commanded Burma Area Army. All of Mutaguchi's divisional commanders opposed key aspects of the plan, and he dismissed all of them during the course of the battle.
Allied transport aircraft, primarily C-47 Skytrains and C-46 Commandos, maintained a continuous airlift into Imphal throughout the siege. By the battle's end, Allied aircraft had flown in 19,000 tons of supplies and 12,000 men, and flown out 13,000 casualties and 43,000 non-combatants. Deliveries included over a million gallons of fuel, 40 million cigarettes and animal fodder for the mules supplying outlying outposts.
The Japanese suffered 54,879 casualties at Kohima and Imphal, including 13,376 dead, plus 920 casualties in preliminary fighting in Assam. Most deaths resulted from starvation, disease and exhaustion during the retreat rather than direct combat. The Allied forces suffered 12,603 casualties.
The Japanese plan relied on capturing Allied supply dumps within three weeks, before monsoon rains made their own supply routes impassable. They failed to achieve those captures, left behind most of their field artillery to ease movement, and underestimated Allied air superiority, which allowed Imphal to be resupplied by airlift despite the land siege. Japanese commanders also concealed the true state of their forces from higher command, prolonging the offensive past the point of recovery.
In 2013 the British National Army Museum ran a public contest in which the combined battles of Imphal and Kohima were jointly voted Britain's Greatest Battle. The two battles together have been recognised as the turning point of the Allied campaign against Japan in Burma. The Commonwealth War Graves Commission established Imphal War Cemetery and Kohima War Cemetery to commemorate British and Indian soldiers who died there.