Operation U-Go begins

On the night of 7–8 March 1944 the regiments of Lieutenant General Genzō Yanagida’s Japanese 33rd Division moved north from the Kalemyo area and the Chin Hills to cut off and destroy the 17th Indian Division defending Tiddim. It was the first move of Operation U-Go (ウ号作戦, “Operation U”), the great offensive of Lieutenant General Renya Mutaguchi’s Fifteenth Army against Imphal and Kohima – two towns on the border between Burma and British India through which ran the only practicable road from the Chindwin valley to Assam. A week later, on 15 March, the army’s main forces – the 15th and 31st Divisions – crossed the river. For the first time in this war the Japanese army was attacking the territory of mainland India with a force of three divisions.

Popular chronologies give the date as 7 March and speak of an “attempted invasion of India” that began a four-month battle around Imphal. As to the substance, that is right. The dates vary by a day or two between sources: Japanese studies state that the 33rd Division went over to the attack on 8 March, in accordance with Mutaguchi’s order of 11 February; some English-language works take the night of 7–8 March, and some as early as 6 March, when the first columns set off. British patrols and detachments of V Force reported Japanese troops in the rear of the 17th Division on 8 March.

Mutaguchi’s plan

Renya Mutaguchi took over the Fifteenth Army in March 1943, when the headquarters of Lieutenant General Masakazu Kawabe’s Burma Area Army was set up in Rangoon. As late as the autumn of 1942, as commander of the 18th Division, he had opposed an expedition to Assam because troops could not be supplied in the mountains and jungle. He changed his mind under the impression made by Orde Wingate’s first Chindit expedition: if British columns could cross mountains he himself had considered impassable, so could the Japanese army. To this was added a conviction he repeated to journalists and subordinates: as commander of the regiment that had opened fire at the Marco Polo Bridge in July 1937, he felt responsible for the war and wanted to deal it a decisive blow.

In his superiors’ plans U-Go was to be a limited operation – a “defence by attack” that would take IV Corps’s base at Imphal, destroy the forces being assembled there and remove the threat of a British offensive into Burma. Mutaguchi had something bigger in mind. After Imphal he wanted to go on into the Brahmaputra valley and cut the railway supplying Stilwell’s front and the airfields from which aircraft flew over the Himalayas to China. In January 1944, according to Japanese war correspondents, he showed them on a map the road all the way to Delhi. This difference of aims between him on the one hand and Kawabe and the staffs in Singapore and Tokyo on the other was never cleared up.

There was no lack of objections. The Fifteenth Army’s chief of staff, Major General Nobuyoshi Obata, a supply specialist, warned that the army could not be fed; in May 1943 he was removed. At a conference in Rangoon at the end of June 1943 and in subsequent war games, officers of the higher staffs pointed out the plan’s weaknesses, but Kawabe did not forbid Mutaguchi to prepare it. The operation’s main opponent on the staff of the Southern Army, Major General Masazumi Inada, was transferred in October. After a war game in Singapore on 23 December 1943 the plan was approved by Field Marshal Hisaichi Terauchi, and Prime Minister Hideki Tōjō – according to an often-repeated anecdote, after questioning a staff officer while taking a bath – gave Tokyo’s consent. The order of Imperial General Headquarters was issued on 7 January 1944.

Three divisions and the Indian National Army

The Fifteenth Army’s plan divided the offensive into several independent thrusts spread across a front more than 200 kilometres long. The 33rd Division was to encircle and destroy Major General David Cowan’s 17th Indian Division near Tiddim and then strike at Imphal from the south. Major General Tsunoru Yamamoto’s force, made up of elements of the 33rd and 15th Divisions with tanks and heavy artillery, was to smash Major General Douglas Gracey’s 20th Indian Division in the Tamu area and approach Imphal from the east by the road over the Shenam Pass. Lieutenant General Masafumi Yamauchi’s 15th Division was to cross the mountains and close Imphal off from the north. The farthest-reaching task fell to Lieutenant General Kōtoku Satō’s 31st Division: through the wild country of the Naga tribes to Kohima, to cut the road from Imphal to Dimapur, the railhead and main supply base of the front.

The three divisions together with army troops numbered, according to the estimates most often given, about 85,000 men. Alongside them went units of the Indian National Army. The Japanese had initially wanted to use it only for reconnaissance and propaganda, but Subhas Chandra Bose, head of the Azad Hind government, to which Tokyo had handed over the Andaman Islands in December, insisted that Indians fight in the front line and be the first to set foot on Indian soil. The Subhas Regiment under Shah Nawaz Khan covered the left flank of the 33rd Division, the Gandhi Regiment was later attached to Yamamoto’s force, and the special Bahadur group went with the Japanese forward units to persuade soldiers of the Indian Army to change sides. Bose believed that his appearance in Bengal would spark an uprising, and the slogan “Dilli Chalo!” (“On to Delhi!”) had been his army’s battle cry since 1943.

The plan’s greatest weakness was supply. Mutaguchi assumed that Imphal would fall within three weeks, and the troops were issued with roughly that much food. After that they were to live on captured British stocks. There were too few lorries – according to Japanese accounts, the Area Army granted less than a fifth of the transport he had asked for – so Mutaguchi devised the so-called Operation Genghis Khan: thousands of cattle, buffalo and goats were to carry loads across the mountains and then serve as meat. Most of the animals died or drowned at river crossings before they reached the troops. The Japanese also left most of their field artillery behind, believing that in the steep mountains around Imphal the British would not be able to use tanks anyway. Everything had to be finished by mid-May, because the monsoon turned the mountain tracks into mud.

The divisional commanders had their doubts. Satō had distrusted Mutaguchi since the factional quarrels in the army in the 1930s; Yanagida, according to accounts, called him a “fool” behind his back; and the gravely ill Yamauchi went into battle in a spirit of fatalism. All three feared that the army would be stranded in the mountains without food if Imphal did not fall quickly.

The British wait on the plain

On the other side stood Lieutenant General William Slim’s Fourteenth Army, part of Admiral Louis Mountbatten’s South East Asia Command. Imphal was defended by Lieutenant General Geoffry Scoones’s IV Corps with three divisions: the 17th near Tiddim, the 20th near Tamu and the 23rd in reserve. From air reconnaissance, radio intercepts and patrol reports Slim and Scoones knew that the Japanese were preparing an offensive. They decided neither to defend the line of the Chindwin nor to forestall the blow with an attack of their own, but to pull the forward divisions back to the plain around Imphal – several dozen kilometres of flat ground with airfields and depots – and to accept battle there. The Japanese would then have hundreds of kilometres of mountain tracks behind them, the British their own stocks, tanks and aircraft. The experience of the Arakan, where in February encircled units of the 7th Division had held out in the “Admin Box” thanks to airdrops, confirmed that this method worked; the same 5th Division that had taken Maungdaw in January was soon to play an important role at Imphal.

Slim, however, misjudged the timing. He expected the attack around 15 March, so Scoones ordered the forward divisions to fall back to Imphal only on 13 March. By then the 33rd Division was already in Cowan’s rear: its 215th Regiment had reached the Tiddim–Imphal road near the depots at Milestone 109, and its 214th Regiment the Tuitum ridge. The 17th Division had to fight its way out, and Scoones used up almost the entire corps reserve to rescue it.

A further surprise for both sides was Operation Thursday. From 5 March gliders and transport aircraft were flying Chindit brigades deep into Burma, behind Japanese lines, to the Indaw area. The commander of the Japanese air force in Burma, Major General Noboru Tazoe, urged Mutaguchi to detach forces to destroy them. Mutaguchi refused: he believed that within a few weeks he would capture the airfields in Assam from which the Chindits were supplied, and the problem would solve itself. Two battalions of the 15th Division earmarked for Yamamoto’s force, however, became bogged down in fighting the Chindits and did not reach the front in time.

The first days of the offensive

On 15 March, on a moonlit night chosen specially for the crossing, the 15th and 31st Divisions crossed the Chindwin on the stretch from Homalin to Thaungdut and entered the mountains. The Japanese columns advanced quickly along tracks the British considered impassable for large units. Their artillery and supplies were carried by porters, mules and even elephants. An Imperial General Headquarters communiqué of 21 March spoke cautiously of crossing the Chindwin “together with the Indian National Army”. Only news from the front of the entry into India led to a special communiqué being issued in Tokyo at Tōjō’s demand – the Prime Minister, under growing criticism after the defeats in the Pacific, needed a success.

On the Tiddim front Cowan began his withdrawal on 14 March, and for the next two weeks his division fought its way north through Japanese road blocks. So within the very first days it became clear that Yanagida would not be able to destroy it in the mountains, as the plan had assumed.

Its place in the war

U-Go was the Japanese army’s last great offensive against the British and its biggest attempt to break into India. The British held Imphal thanks to an airlift: Mountbatten, on his own responsibility, took transport aircraft off the China supply route, and in the second half of March the 5th Indian Division was flown in from the Arakan. From April Imphal and Kohima were under siege; in May the monsoon came, and the Japanese divisions, which were supposed to live off captured supplies, began to starve. Mutaguchi removed all three divisional commanders one after another, and at the end of May Satō, against orders, withdrew the 31st Division from Kohima. On 22 June British columns from the north and south met on the Kohima–Imphal road, and on 3 July Mutaguchi called off the operation.

The retreat across the mountains in the rainy season turned into a catastrophe. According to the estimates most often cited, the Fifteenth Army lost more than 50,000 men in the operation, of whom some 30,000 were killed or died, mostly of starvation, malaria and dysentery; Japanese and British figures differ in detail. British and Indian losses amounted to about 17,000 killed, wounded and missing. It was the Japanese army’s greatest defeat on land up to that time. Mutaguchi was relieved on 30 August 1944. The Indian National Army lost most of the men it had sent to the front, and Bose’s hopes of an uprising in India came to nothing.

The defeat at Imphal and Kohima reversed the situation in Burma. Japan used up forces there that it later lacked for the defence of the country, and at the end of 1944 Slim’s Fourteenth Army advanced south across the Chindwin; in May 1945 the British recaptured Rangoon. Mutaguchi’s plan to cut off the air route to China and threaten the Ledo Road produced the opposite effect – it opened the way for the Allies to retake Burma.