Study Guides

WWII in the Pacific

Raising the flag on Iwo Jima. Photograph by Joe Rosenthal


Japan in the decade preceding World War Two had become increasingly imperialistic, with worship of Emperor Hirihito on the rise and the army becoming an increasingly political body. Expansion begun as early as 1931, with the invasion of Chinese Manchuria, making it a puppet state. This was seen as brazen disregard of the League of Nations, a precursor to the UN, increasing tensions between Japan and the West.

Japan looked further, identifying the Dutch Indies, now Indonesia, as a key target due to their oil reserves in 1935. Another puppet state was created in Inner Mongolia in 1936, and a full invasion of China began in 1937. In 1939, Japan invaded the Soviet Union but was soundly defeated in the Battle of Khalkhin Gol. In September 1940, Japan seized French Indochina (modern Laos, Cambodia and Vietnam), and singed a treaty with the Axis forces of Germany and Italy. To stop this imperialist expansion, America, Britain, Australia, Holland and China banned the export of oil to Japan, known as the ABCD (American-British-Chinese-Dutch) lines. These imports made up 80% of Japan’s consumption; they were essential and hence in Japanese minds, war was guaranteed.

Japanese Plan

The Japanese plan of war depended on a weak reaction from the UK, Soviet Union, and other European powers due to their ongoing war with Germany. Accordingly, a neutrality pact was signed with the Soviet Union in 1940. The Japanese believed the USA would inevitably become involved (although this has since been debated) and so planned for a fast, strategic war.

Total victory and occupation of the USA was impossible. Instead, Japan hoped to take key targets in two operational phases. The first focused on the South-East Pacific and the capturing of the Dutch Indies, British held Malaya Hong Kong, and Singapore and the US held Philippines, to escape the crisis of the ABCD lines. They then planned to expand as far as Fiji, Samoa, Midway and the Aleutian Islands. To do this, a shock attack on Pearl Harbour, America’s main Pacific military base in Hawaii, would paralyse the US Navy whilst the perimeter was secured. By holding all major islands in the Pacific, the Japanese hoped to block any attempt to launch a counter-attack and could squeeze the US into a surrender.

Japanese Invasion of China

"Bloody Saturday" by H.S. Wong. baby Ping Mei amid the destruction of Shanghai South Railway Station

“Bloody Saturday” by H.S. Wong. Baby Ping Mei amid the destruction of Shanghai South Railway Station

Japan controlled Manchuria after their invasion in 1931 but had also increased influence into Northern China. Puppet states had been set up in areas such as Tongzhou, a district of Beijing, with a Japanese garrison. China was also subject to a number of ‘Unequal Treaties’ in which several nations were granted occupation of parts of Chinese cities. Japan was allowed to station guards along the railway to Beijing, as were other European nations, but had increased that number to over 7,000, well beyond the limits set the in the Boxer Protocol.

An incident at the Marco-Polo Bridge near Beijing, led to an escalation and Japanese invasion and occupation of Beijing and Tianjin. Despite Japan’s contentment with occupation of Beijing, China had had enough. Chinese resentment is shown in the mutiny of the troops of the

Japanese puppet state in Tongzhou and the setting fire to the Japanese section of the city, in which 200 Japanese civilians died. The KMT, Chinese Nationalist government, also surrounded the Japanese section of the Shanghai Occupied Area, and on August 14, accidentally bombed it, resulting in 3,000 civilian deaths.

A full-scale invasion of China began, but Japanese casualties were much higher than expected. The Civil War between the KMT and Communists in China had been suspended to face the common Japanese threat. 200,000 men, several war vessels and strong airpower was needed to take Shanghai in a 3-month long siege. Japan flooded China with men, committing 350,000 to the taking of the Chinese capital, Nanjing. Following its fall, there occurred the ‘Rape of Nanjing’, in which the Japanese are estimated to have killed up to 300,000 Chinese, mostly civilians, whilst also committing extensive rape and looting.

The advance continued with great momentum, as Wuhan, the new KMT capital, Kaifeng, capital of Henan province, and later French Indochina fell. The KMT retreated to Chongqing, and to stop the Japanese advance destroyed the Huayuankou dike on the south bank of the Yangtze. Up to 800,000 civilians and soldiers on both sides drowned; 10 million became homeless. Here most of the Japanese advance halted. Japan struggled to hold a Chinese territory so full of resentment and the Chinese managed to launch a counter-offence with minor success. A stalemate was reached but Japan held most of the Chinese coast and North.

Outbreak of War with the West

USS Arizona Memorial at Pearl Harbour

USS Arizona Memorial at Pearl Harbour

On the 7 December 1941 (8 in East Pacific), Japan launched attacks without warning with both its navy and army on Hong Kong, Malaya, the Philippines, Hawaii, Wake, Guam and Thailand. The largest attack fell on the US Naval base of Pearl Harbour on Hawaii. Casualties were substantial: 8 battleships, 188 aircraft and 2,403 American soldiers. However, the crucial aircraft carriers were at sea, and most of the base facilities weren’t damaged. Far from disabling the US fleet into submission, Japan had sparked fury in the US at the unprovoked and undeclared attack.

The US, UK, Canada, Holland and Australia declared war within two days. Germany and Italy in turn declared war on the US, even though Japan would give little aid to the European war whilst America would be of vital importance.

South-East Asia Advance

Despite the relative failure of the Pearl Harbour attack, Japan’s speed of expansion was extremely effective. Thailand surrendered within 5 hours, even allying with Japan on 21 December, allowing access to European colonies in Malaya. By Christmas 1941, Hong Kong, Wake, Guam and Penang had all fallen.

On 1 January, the Allied forces were united in the American-British-Dutch-Australian Command (ABDACOM), under the leadership of Sir Archibald Waver, a British general. But the Japanese momentum continued with invasions into Burma, the Dutch Indies, New Guinea and the Solomon Islands.

Lieutenant-General Arthur Ernest Percival leads the British forces to surrender to the Japanese in Singapore

Lieutenant-General Arthur Ernest Percival leads the British forces to surrender to the Japanese in Singapore

On 15 February 1942, Britain suffered what Winston Churchill called ‘the worst disaster’ in British military history as its major base in the Pacific, Singapore, surrendered, in which 80,000 British, Indian and Australian troops were captured.

Japan expanded further even bombing Darwin in Australia in the largest attack on Australia by a foreign power in history, killing 243 people. It would be the first of over 100 air raids. In the Battle of Java Sea, Japan defeated the main allied navy and as a result the forces in Malaya surrendered on Java and Sumatra. Japan raided into the Indian Ocean, sinking the HMS Hermes aircraft carrier and targeting bases in Ceylon, pushing the British Navy out of South East Asia.

Burma had become occupied as Britain retreated to the Indian border but the territory would remain disputed, with the Chinese aiding the British, for example at the Battle of Yenangyaung, where 7,000 trapped British soldiers were rescued by the Chinese.

Fall of the Philippines

In March, America suffered a great defeat in losing Manila the Philippines. The islands were under the command of General Douglas MacArthur, a charismatic figure famous for his corn-cob pipe. He felt a strong personal duty to the Philippines and so when Roosevelt ordered his smuggling out of the islands in order to be able to continue his command of the American forces in the South-West Pacific, he delivered the famous words “I came through and I shall return”, which he refused to change to ‘we will return’ despite being asked to do so by the government. On April 9, Bataan, the last US holding in the Philippines. 76,000 Allied soldiers were captured and were forced in the ‘Bataan Death March’, an 106km march to Camp O’Donnell in which it is estimated between 5,000 and 18,000 Filipinos and 500 and 650 Americans died.

Failure of the Second Operational Phase

With the fall of the Philippines and British colonies, Japan had completed its first operational phase, and begun to move toward its second. The Allies had begun something of a counter-attack, making use of their aircraft carriers, bombing the Marshall islands, Wake and Marcus Island and Rabaul from land-based aircraft.

Japan desired to cut off Australia as a possible base for an offensive. Some generals in the Japanese Navy proposed an invasion but the Army refused as they were too committed in Manchuria and afraid of a Soviet invasion. Instead, the option was taken to cut off Australia by taking New Caledonia, Fiji, Samoa, eastern New Guinea and the western part of New Britain (together now Papua New Guinea), and from there threaten Australia by air. Midway Island and the Aleutian Islands were also targeted to pressure America and their Navy by removing possible advance bases.

However, Allied morale was slightly restored in April by the Doolittle raid, an ineffective but symbolic bombing raid on Tokyo by 16 bombers. In May, the battle of the Coral Sea, despite the Japanese sinking one US carrier and disabling another, was a victory for the Allies and they repelled the Japanese invasion of Port Moseby, capital of New Guinea. Moreover, none of the three Japanese carriers

involved could be used at Midway. In this battle, neither fleet sighted each other but fought from range and with aircraft, indicative of how important carriers would become.

Allies Regroup

The Japanese cancelled further attacks on Fiji and Samoa and focused all attention on the North Pacific, aiming to take Midway, pressuring the US Navy into surrender. The Japanese outnumbered the Americans with 4 heavy carriers to America’s 3, 3 light carriers to none, 11 battleships to none, 44 destroyers to 18, but America fielded 19 submarines to Japan’s 15, and could use land-based aircraft from Midway. Despite this, American carrier bombers sunk all four of the Japanese heavy carriers, only losing the Yorktown carrier in return. Midway is commonly held as the turning point of the Pacific War, with the Japanese momentum dramatically halted and her naval offensive capabilities nullified by her loss of her carriers, though her defensive air capabilities remained via land-based aircraft.

Coastwatcher aptain W.F. Martin Clemens with members of the Solomon Island Police Force

Coastwatcher Captain W.F. Martin Clemens with members of the Solomon Island Police Force

The war now became a series of bitterly contested conflicts. In July 1942, Japan landed on Guadalcanal in the Southern Solomon islands and started building an airbase but were spotted doing so by Allied Coastwatchers. These were intelligence officers stationed on Pacific islands, sometimes aided by the locals, who supplied information to the Allies, especially later in the battle giving early warning of Japanese air raids.

On 7 August, the Allies launched their first major offensive and took the airfield and the strategic Tulagi harbour within a day via an amphibious landing. However, the Japanese countered decisively on the night of 8-9 August during the naval battle of Savo Island. Five allied cruisers and two destroyers were lost whilst only mildly damaging one Japanese cruiser. This would start a long battle of attrition in which, by January, Allied losses rose from around 14,000 to 44,000, Japanese from 7,000 to 22,000.

Wrecks in the Ironbottom Sound, W.wolny, Wikimedia Commons

Wrecks in the Ironbottom Sound, W.wolny, Wikimedia Commons

So costly was the battle to both sides that the sea north of Guadalcanal became known as ‘Ironbottom Sound’ as so many ships (an estimated 50+) were sunk there during the battle. The US Navy commemorates the area annually by laying wreaths, and many sailors still pass the area in silence. In the Naval Battle of Guadalcanal, the only two US admirals lost in a surface engagement in the entire war died. In total, the Allies lost 2 carriers and 22 other vessels, but the Japanese lost over 20,000 men and after losing the vital Naval Battle of Guadalcanal, decided to withdraw from the island. Momentum was now with the Allies.


China Regroups

In China, the Japanese had also slowed, with their first major defeat of the war occurring at Changsha in Hunan. The conflict was bloody. Operation Sei-go was a mission launched by the Japanese in July 1942 to capture the Allied pilots of the Doolittle raid who had parachuted into the provinces of Zhejiang and Jiangxi and were mostly hidden by Chinese civilians. The Japanese launched a campaign of retribution, burning Chinese towns and using biological warfare by spreading cholera, typhoid, dysentery pathogens and contaminating food and wells with paratyphoid and anthrax. Around 10,000 Japanese soldiers fell ill from their own biological weapons, and 1,700 died, but Chinese civilian casualties numbered around 250,000.

The British continued to flounder in Burma through the embarrassing defeat of the Arakan offensive, not helped by a famine in Bengal causing up to 3 million deaths. But China continued to succeed in the Battle of Changde. The Japanese captured the city on December 6 but only after over a month of tough fighting, and the Chinese 57th Division held the Japanese pinned in the city for enough time that other Chinese forces were able to surround the city and forced a Japanese withdrawal. It was a victory in particular for the Chinese air-force, previously too easily defeated, who had been helped by Witold Urbanowicz, the second highest-scoring Polish Ace in the Battle of Britain.

A Turning Point in India and Burma

The Allies regrouped under Admiral Lord Louis Mountbatten, and with US troops, began constructing the Ledo Road to link India with China. In reaction, Japan launched Operation U-go in March 1944, a large offensive on Allied positions at Imphal and Kohima in India. The British were bolstered by the firm Indian divisions of XV Corps and the Japanese attack on both targets was repelled. Without an early victory, supplies over the forested and mountainous terrain failed. Japan lost over 50,000 troops, her greatest defeat yet, but mostly to disease and starvation. The US troops advanced north in Burma, aided by the Chindits, a unit of British, Burmese and Ghurkha battalions, that worked deep behind enemy lines in difficult conditions. The Chinese invaded Northern Burma and over the course of 1944- 5, would link up with American forces. Allied advance was then gradual but consistent, capturing Rangoon in May 1945 and preparing to advance to Malaya when surrender occurred.

Allied Island Hopping 1943-4

After Midway, the Allies and especially America turned to a policy of mass-industrialisation, replenishing their navy and air force. Japan lacked the industrial base to do the same. The Allies began a policy of ‘Island-Hopping’, taking islands one at a time, or at least neutralising their offensive capabilities without capturing in examples such as Truk or Formosa. First to fall were the Gilbert and Marshall Islands, in which the Allies greatly improved their tactics of amphibious invasions and exposed the over-extended Japanese island garrisons.

The Allied forces now targeted the Mariana Island and Palau. It involved an ambitious amphibious operation, juxtaposed by the D-Day landings in the same month (June 1944), over 1,000 miles from a permanent US base. Despite heavy bombardment, the Japanese forces were largely unaffected, and victory was won by a hard-fought infantry engagement. American troops were armed with flame-throwers and demolition charges to maximise damage but in doing so unleashed horrific conflict. On the night of 6-7 July, the pocketed groups of Japanese banded together in the largest Bonsai attack of the war, a 4,000 strong suicidal charge. The Japanese civilians on the island of Saipan committed suicide by jumping off cliffs to the north.

The capture of the Marianas allowed B-29 bombers to be stationed within range of Tokyo and, when the news arrived, the Japanese Prime Minister and his cabinet resigned. It was viewed by many as the last Japanese defence before the homeland.

Re-Occupation of Philippines

General MacArthur walks ashore at Palo, Leyte.

General MacArthur walks ashore at Palo, Leyte.

Holding Saipan was seen as a priority by the Japanese and so followed in June 1944 the largest carrier battle of the war and history in the Philippine Sea. It was a catastrophic defeat for the Japanese. 3 of its 9 carriers were sunk to none of the American 15. Even more damaging though was the loss of around 90% of its air-force from strong anti-air guns, and effective American bombing of their land air-fields.

It was decided to make one more all-out attack in October 1944 in order to prevent the Allied occupation of the Philippines. The aim was to draw out the US carrier group with 4 of their remaining carriers by sailing North to open sea. Two strong fleets of the remaining battleships and heavy cruisers would then converge on Leyte Gulf and destroy the American beachhead there. The diversion succeeded, and the Japanese carrier aircraft inflicted some damage through the first use of kamikaze aircraft, but in the end the entire force was sunk. The sacrifice did not work. The two main forces failed to take the beachhead, and suffered heavy losses including the Musahi, one of Japan’s two flagship battleships. The Battle of Leyte Gulf, argued by some as the largest naval battle in history, was a catastrophic loss for Japan.

Occupation of the Philippines was now near inevitable but progress was still bitter and slow. Luzon, the largest island in the Philippines, involved ten US divisions and five independent regiments, more US troops than any other conflict of the war, and 250,000 Japanese troops, of which 80% died. Hiroo Onoda, an intelligence officer, only surrendered on 9 March 1974 after hiding out for 29 years, relieved by his former commander after an order from the Emperor Showa. Despite MacArthur’s refusal to allow aerial bombardment in order to protect civilians, Manilla fell on 4 March 1945 and MacArthur kept his promise to return and liberate the Philippines.


Japanese-Americans arrive for internment processing.

Japanese-Americans arrive for internment processing.

During the war, around 120,000 Japanese-Americans who were residing on the west coast of America were “interned” in ten different camps. Families were kept together but conditions were hard with internees staying in military style barracks that were over-cramped and unsuitable for family living. Incidents of internees being shot were rare but did happen, such as the case of James Wakasa.

However, Japanese-Americans still played a great role in the American services. 33,000 served, of which 20,000 joined the army. The Japanese-American units achieved great success: the Military Intelligence Service was vital in deciphering the ‘Z Plan’, the Japanese plans to defend Saipan; the 522nd Field Artillery Battalion liberated the Dachau concentration camp in Germany; and the 442nd Infantry regiment became the most decorated unit in US history earning more than 18,000 awards in two years.

In 1988, President Reagan opened an investigation of the legality of internment, which concluded there was insubstantial evidence of any security risk posed by these Japanese-Americans, and interment was instead a product of racism. $20,000 dollars was agreed as compensation to each internee and the US government eventually dispersed more than $1.6 billion.


The war was now entering its final stages. The final major campaign in the South-West Pacific was the capturing of Borneo. Australian troops invaded the nearby island of Tarakan on May 1 1945, and over the course of June and July attacks were mounted on the island proper. The campaign was criticised as unnecessary, but it did break the Japanese supply of oil and liberate several POW camps, including Sandakan in which only 6 of 2,500 prisoners survived.

Iwo Jima and Okinawa

Attacks moved onto Okinawa and Iwo Jima, two Japanese home islands to the south of Japan itself. Both were key for stationing planes in order to defend against the American B-29 bombers aimed for Japan. And Okinaway was selected as the vital staging post for an eventual invasion of Japan. Japan resorted to forcing unacceptably high casualties for the Allies in order to discourage further advance.

Raising the flag on Iwo Jima. Photograph by Joe Rosenthal

Raising the flag on Iwo Jima. Photograph by Joe Rosenthal

At Iwo Jima, the Japanese dug in, their command being under 10m of concrete, rendering preinvasion bombardment ineffective. They also resorted to kamikaze tactics as the air-force began to run out of skilled pilots. Despite the inevitability of defeat, the Japanese were fierce and this was the only battle in which American casualties at over 26,000 (killed and wounded) totalled more than Japanese at around 18,000. On February 23, 1945 six American soldiers raised the US flag over Mount Suribachi marking victory and the photo taken of them would become one of the most iconic of the entire war.

Okinawa was even fiercer. Referred to in Japanese as etsu no bōfū (“violent wind of steel”) due to ferocity and high number of vehicles in the conflict, it was one of the bloodiest of the war. Half the total civilian population of 300,000 went missing, died or committed suicide, and there were over 160,000 combined casualties on both sides. Simon Bolivar Buckner Jr. was commander of the US infantry on the island, and was killed in action, being the highest-ranking US officer to do so until the 9/11 attacks. The Japanese made wide use of suicide tactics, including bomb laden gliders and the one-way mission of the battleship Yamato. On July 2 1945, the island was declared as won. 94% of the Japanese defenders died.

Atomic Bombs

The campaigns of Iwo Jima and Okinawa showed invading Japan would be a very costly affair. Since 1942, partly due to Einstein’s warning in 1939 of the dangers of Germany doing the same, the Manhattan Project had been started to develop nuclear weapons. Fire-bombing became widespread, one napalm strike on Tokyo in March 1945 killing over 100,000 people, more than either later atomic bomb, but Japan would not surrender and so the Potsdam Declaration by Churchill, Truman and Chiang Kai-shek was issued in July 1945: surrender or face “prompt and utter destruction.”

The Hiroshima atom bomb cloud 2–5 minutes after detonation

The Hiroshima atom bomb cloud 2–5 minutes after detonation

On 6 August 1945 the US dropped an atomic bomb on the city of Hiroshima, and on 9 August on Nagasaki. An estimated 140,000-290,000 would eventually die of these attacks due to the effects of radiation, of which 120,000 died immediately. The site is now a Peace Memorial Site.

End of War

The devastation of these bombs stunned the Japanese leadership and it took the second bombing for their repercussions to truly be believed. On top of this, on 8 August, the Soviet Union invaded Manchuria. On 10 August, Japan agreed to accept the conditions of the Potsdam Declaration, and on 15 August, known as V-Day in the East, victory was finally declared. The official treaty was signed onboard the USS Missouri, docked with more that 250 other allied ships in Tokyo Bay, on 2 September.

MacArthur took over the occupation of Japan, of which the Soviet Union was allowed very little influence. Emperor Hirohito remained on the imperial throne but his powers were strictly limited by law, the Japanese cabinet was completely changed and became a democracy. Initially, Japan was treated as a dangerous enemy and America tried to undermine any chance to regain strength. But with the growing cost of occupation and the Cold War, American perception of the enemy changed. The occupation ended in 1952 and sovereignty was fully restored.

European power in the Pacific had also been irreversibly dented, and the colonial powers would gradually withdraw nearly entirely.

War Crimes

The International Military Tribunal for the Far East took place in Ichigaya, Tokyo from 29 April 1946 to 12 November 1948. This was to try and condemn Japanese war criminals in the Pacific conflict.

American and European powers suffered the undeclared attacks on 7 December 1941, and the Japanese POW camps were notorious. The infamous Burmese Railway cost 12,000 allied prisoners, and 90,000 civilians their lives subject to terrible conditions, disease, and execution. The death rate of POWs was 27%, 6 times that in German or Italian camps.

The Chinese suffered even worse. Some 200,000 ‘comfort women’ were forced into prostitution for the Japanese army, a fact denied even by the Japanese Prime Minister in 2007. The Rape of Nanjing resulted in 300,000 civilian deaths and widescale rape. Biological and chemical warfare was estimated to have killed 300,000-400,000 civilians. Unit 731 was a research unit that conducted various experiments of Allied and civilian prisoners, including vivisection, biological weaponry, forced impregnation, syphilis, and frostbite. Perhaps most shocking of all, the researchers of the unit were given immunity by the US government in secret, in exchange for their results.