Operation U-Go

• 1. Introduction

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  Operation U-Go began on the 6th of March, 1944, when Japanese forces crossed into northeast India on one of the most audacious bets of the Second World War. The man behind it, Lieutenant-General Renya Mutaguchi, had once called this same terrain impassable. He had told his superiors the jungle-covered mountains separating India and Burma were too difficult, the logistics impossible. Years later, commanding the Fifteenth Army himself, he had reversed his position entirely and staked tens of thousands of lives on proving himself wrong.

  The offensive aimed at the Brahmaputra Valley, cutting through the towns of Imphal and Kohima. If it succeeded, the Allies' supply lines to northern Burma would be severed, and the airfields feeding Nationalist China would be cut off. If it failed, the Japanese forces in Burma would be left shattered, starving, and exposed. What drove Mutaguchi to launch an attack that his own divisional commanders called reckless? Why did Prime Minister Hideki Tojo give his blessing from a bathtub? And how did an army that began the campaign with momentum end up abandoning its artillery and leaving its sick behind in the jungle?

• 2. Mutaguchi's Reversal

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  In late 1942, Lieutenant-General Renya Mutaguchi had been one of the loudest voices against invading India. He told Lieutenant General Shojiro Iida that the terrain was too difficult and the supply problems impossible to overcome. His opposition was firm and practical.

  What changed his mind was partly shame. Mutaguchi later discovered that Imperial Army HQ had originally been the source of the invasion idea, not just local commanders. He had been embarrassed at his own earlier caution, believing he had blocked a plan sanctioned from the very top.

  The British general Orde Wingate pushed him further. In early 1943, Wingate's Chindit long-range penetration force had moved through terrain that Mutaguchi had specifically claimed was impassable to the 18th Division he then commanded. The Allies publicised the Chindits' successes while concealing the severe losses to disease and exhaustion the expedition had suffered. Mutaguchi drew the wrong lesson. He became convinced that the mountains and jungle were no barrier after all.

  By the time Mutaguchi took command of the Fifteenth Army, his ambitions had grown well beyond tactical gain. He believed it was his destiny to win the decisive battle of the war for Japan. His career stretched back to the Marco Polo Bridge incident of 1937, and he felt the weight of that history pressing him forward.

• 3. A Plan Approved From the Bath

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  Between the 24th and the 27th of June, 1943, a planning conference in Rangoon first put Mutaguchi's ideas formally on the table. Major General Todai Kunomura, his Chief of Staff, presented the proposal. The reaction was hostile. Staff officers from Burma Area Army felt Kunomura was overstepping, and senior figures including Lieutenant General Eitaro Naka, Major General Masazumi Inada, and even Lieutenant General Gonpachi Kondo from Imperial General Headquarters catalogued the plan's tactical and logistical weaknesses.

  Yet the plan survived. The man who might have killed it, Lieutenant General Masakazu Kawabe, declined to forbid Mutaguchi from pursuing the idea. At later exercises in Maymyo and in Singapore, Naka shifted toward support. Inada held out longer. He floated an alternative: attack the Chinese province of Yunnan instead. On the 11th of October, 1943, Inada was removed from Southern Expeditionary Army, made a scapegoat for unrelated failures involving territorial concessions to Thailand under Field Marshal Plaek Pibulsonggram. His departure cleared the last significant internal obstacle.

  After a map exercise in Singapore on the 23rd of December, 1943, Field Marshal Hisaichi Terauchi formally approved the operation. Inada's replacement, Lieutenant General Kitsuju Ayabe, was sent to Imperial Army HQ to secure final approval. Prime Minister Hideki Tojo gave that approval after questioning a staff officer about the plan while sitting in his bath. Once the decision was made, neither Terauchi nor Kawabe could call it off.

• 4. The Indian National Army

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  Subhas Chandra Bose shaped Operation U-Go in ways that went beyond military planning. Leader of the Azad Hind movement and commander in chief of its armed wing, the Azad Hind Fauj, Bose was determined that the Indian National Army would march into India alongside the Japanese.

  The INA drew its fighters mainly from former prisoners of war captured by Japan after the fall of Singapore, alongside Indian expatriates across Southeast Asia who had joined the nationalist cause. Bose argued to Japanese commanders that a victory like the one Mutaguchi envisioned would cause British rule in India to collapse from within. That argument appealed to Mutaguchi and Tojo.

  Japanese planners had originally earmarked the INA for auxiliary roles only: reconnaissance and propaganda work, not front-line combat. At Bose's insistence, that calculus changed. Two INA brigades were assigned to the attacks on Imphal from the south and east. For Japan, there was a broader ideological framing available: the idea that Japanese expansion into Asia supported Asian self-determination against western colonialism. Whether that framing was sincere or convenient, it gave the operation a political dimension that purely military arguments could not supply.

• 5. Four Attacks, One Gamble

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  Mutaguchi's plan assigned four separate forces to converge on Imphal and Kohima, widely spread across extremely difficult terrain. The 33rd Infantry Division under Lieutenant-General Motoso Yanagida was to destroy the 17th Indian Infantry Division at Tiddim and strike Imphal from the south. Yamamoto Force, assembled from detachments of the 33rd and 15th Divisions and commanded by Major-General Tsunoru Yamamoto, with tank and artillery support, would neutralise the 20th Indian Infantry Division at Tamu and hit Imphal from the east.

  Lieutenant-General Masafumi Yamauchi's 15th Infantry Division would encircle Imphal from the north. In a separate but linked operation, Lieutenant-General Kotoku Sato's 31st Infantry Division would seize Kohima and then push on to capture the major Allied supply base at Dimapur in the Brahmaputra Valley.

  The staff at Burma Area Army thought the separation of forces was dangerously wide. Several officers who said so were transferred. Mutaguchi's own divisional commanders were privately skeptical, believing he was gambling that early battlefield success would resolve supply problems that had not actually been solved. Some called him a blockhead. Before the first shot was fired, the operation depended on everything going right quickly, because the Japanese forces would carry only enough supplies to last a matter of weeks.

• 6. The Allied Preparation

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  Lieutenant General William Slim commanded the British Fourteenth Army in early 1944, and the force he led into the battle was substantially better than the one that had failed in an earlier Arakan offensive. Over the preceding year, Slim and his predecessor General George Giffard had worked to rebuild the health, training, and morale of British and Indian units through better rations, improved medicines, and cleaner administration in rear areas.

  Slim and Lieutenant General Geoffry Scoones, who commanded Indian IV Corps at Imphal, had gathered enough intelligence to know a Japanese offensive was coming. What they lacked was precise knowledge of Japanese objectives, and the opening moves would catch them partly off-guard. Slim's chosen response was not to attack across the Chindwin River first, nor to defend the river line. Instead, he planned to draw the Japanese toward Imphal, where their supply lines would become impossibly stretched.

  One key Allied capability the Japanese had failed to account for was air supply. The Allies had developed methods for supplying cut-off units by aircraft, which allowed encircled formations to hold positions that would otherwise have to be abandoned. That capability would prove decisive during the weeks of fighting ahead.

• 7. Imphal, Kohima, and Collapse

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  The diversionary Ha Go attack in the Arakan began on the 5th of February, 1944. Japanese forces from the 55th Division overran an Indian divisional headquarters and isolated forward units. When they pressed against a fortified position known as the Admin Box, they found that Allied aircraft kept the garrison supplied while the Japanese themselves ran out of food. British and Indian forces broke through to relieve the defenders, and the Japanese withdrew, starving.

  The main offensive opened on the 6th of March. Slim and Scoones had ordered their forward divisions to fall back, but the orders came too late for the 17th Indian Division, which was cut off and had to fight its way back to the Imphal plain. Scoones committed nearly all his reserves to help them. The Allies flew an entire division, including its artillery and transport, from the Arakan front to Imphal in time to stop the Japanese 15th Division from overrunning the town from the north.

  At Kohima, the Japanese 31st Division fought for control of a ridge dominating the Dimapur-Imphal road from the 3rd to the 16th of April. A small British force held until relief arrived on the 16th of April. Indian XXXIII Corps then counter-attacked from the 18th of April to the 16th of May to retake the lost positions. By late May, with his men starving, Lieutenant General Sato defied Mutaguchi's orders to hold and withdrew his division. XXXIII Corps drove south and linked with the Imphal garrison on the 22nd of June, reopening the road and ending the siege.

  Mutaguchi ordered further attacks through late June, but his formations were no longer capable of obeying. On the 3rd of July, he formally called off the offensive. The Japanese fell back toward the Chindwin, abandoning artillery, vehicles, and soldiers too sick to walk.

• 8. The Reckoning

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  The scale of the defeat was without precedent for the Japanese Army in Burma up to that point. British and Indian forces had suffered around 16,987 dead, missing, and wounded. The Japanese counted 60,643 casualties, including 13,376 killed. The majority of those losses came not from combat but from starvation, disease, and exhaustion, the same logistical vulnerabilities Mutaguchi's own commanders had warned him about before the offensive began.

  Mutaguchi sacked all three of his divisional commanders during the operation itself, before the army had even finished retreating. On the 30th of August, he was dismissed in turn. Lieutenant General Kawabe, whose health had broken under the strain, was also removed. Senior staff officers across Fifteenth Army and Burma Area Army were transferred out to lower commands at divisional and regimental level.

  Sato's defiance at Kohima stood as a rare public rupture within the Japanese chain of command. He had withdrawn his starving division against direct orders, accepting the personal consequences rather than sacrifice what remained of the 31st Division. The man who had called the plan reckless from the beginning had found, at the end, that the only way to save his soldiers was to act on that judgment.