How Japan Invaded Thailand during World War II

The Japanese invasion of Thailand during World War II took place on December 8, 1941, just hours after the attack on Pearl Harbor. It was the first major military campaign in Southeast Asia by the Japanese and marked the beginning of their expansion into the region.

The invasion was significant as it allowed Japan to secure access to key resources in Southeast Asia and establish a foothold in the region, which would become a major battleground in the war.
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The Invasion of Siam

After Thailand failed to respond to Japan's ultimatum, Japanese troops invaded Thailand from Indochina. They landed south of Bangkok and at various points along the Kra Peninsula several hours later.

The primary battles and resistances of how Japan invaded Thailand:

  1. In Hat Yai (Songkhla), where the Thai military suffered casualties. Reports indicate that 15 Thai soldiers lost their lives in the confrontation, with eight killed in action from the 41st Infantry Battalion and seven from the 5th Infantry Battalion. Additionally, between 30 to 55 soldiers were wounded during the battle. 
  2. In Pattani, the 42nd Infantry Regiment of the Imperial Japanese Army's 5th Division, led by Major Shigeharu Asaeda, proceeded with their landings and faced the Thai 42nd Infantry Battalion, Pattani Provincial Police, and Thai Yuwachon Thahan units (including the 66th Yuwachon Thahan Training Unit from Benjama Rachoothit School). The Thai battalion commander, Khun (ขุน) Inkhayutboriharn, was killed in action, along with 23 other soldiers, five Provincial Police officers, four Yuwachon Thahan members, and nine civilians.
  3. In Prachuap Khiri Khan around 03:00, the Japanese 2nd Infantry Battalion of the 143rd Infantry Regiment, led by Major Kisoyoshi Utsunomiya, landed and overran police resistance to occupy the town. The Thai airmen and Prachuap Khirikhan Provincial Police held out until midday. The Japanese casualties were estimated at 115 dead by the Japanese and 217 dead and over 300 were wounded by the Thais. The Thais suffered 37 dead and 27 wounded.
  4. In Don Muang (Samut Prakan), the Don Muang Royal Thai Air Force Base was attacked by the Japanese air force. The base was defended by the Thai air force, but they were outnumbered by the Japanese. The attack resulted in the loss of six fighter planes belonging to the Thai air force.

Eventually, an armistice was ordered and the fighting stopped at noon. The Japanese military campaign in Thailand was swift and decisive. They faced little resistance from the Thai military, who had been ordered by the government to avoid any conflict with Japan.

  • The Japanese demanded and received unrestricted access to Thai territory, which included airfields, ports, and railway lines.
  • The Thai government, led by Field Marshal Plaek Phibunsongkhram, decided to cooperate with the Japanese in order to avoid being invaded. (When it was clear that Japan was losing the war, Phibun was dumped in favor of the civilian, Khuang Apaiwong on 31 July 1944)

On August 6th and 9th, 1945, the cities of Hiroshima and Nagasaki were devastated by two atomic bombs dropped by the United States during World War II. While they have been rebuilt and modernized, the question is about the safety of Hiroshima and Nagasaki after the bombing.

Relationship between Japan and Thailand before World War II

3 years before World War II (December 1938), Phibunsongkhram took power in Thailand as a military dictator. Phibunsongkhram, also known as Phibun, maintained friendly relations between Thailand and Japan.

  • In January 1941, Japan acted as a mediator between the French and Thai governments to secure access to the ports and air bases in French Indochina. This occurred almost a year before the outbreak of World War II.
  • By mid-1941, Field Marshal Phibun sought assurances of support from Britain and the United States in the event of a Japanese invasion of Thailand. However, neither country was able to provide these guarantees. While British Prime Minister Winston Churchill supported a public warning to Japan that an invasion of Thailand would result in a British declaration of war, the United States was not willing to agree to this. Consequently, Britain was not prepared to take unilateral action.
  • On the same day that Field Marshal Phibun reached an agreement with the Japanese, the British informed him that an invasion of Thailand by the Japanese was likely imminent. In response too late, Prime Minister Winston Churchill sent a message to Field Marshal Phibun advising him to defend Thailand if attacked. Churchill emphasized that the preservation of Thailand's true independence and sovereignty was of British interest and that an attack on Thailand would be seen as an attack on Britain itself.

Phibun attempted to maintain a friendly but noncommittal stance towards Japanese officials who were urgently lobbying his government for support. However, after the Japanese attack on Pearl Harbor and the impending invasion of Thailand on December 8th, 1941, the Thai government was forced to seriously consider all options. At a cabinet meeting on that day, four main options were discussed.

  1. Japan and Thailand would conclude an offensive/defensive alliance.
  2. Thailand would join the Tripartite Pact with Germany, Italy, and Japan.
  3. Thailand would cooperate with Japanese military operations.
  4. Thailand and Japan would undertake the mutual defense of Thailand.

Each option included the expectation that Japanese forces would be allowed to pass through Thailand, and Japan offered to assist Thailand in recovering its lost territories with each option.


The Japanese invasion of Thailand was a significant event in World War II, marking the beginning of Japan's expansion into Southeast Asia. The invasion had a profound impact on Thailand and its people, leading to widespread suffering and exploitation. While the legacy of the invasion remains a sensitive issue, Thailand and Japan have developed a strong relationship in the post-war period, built on mutual respect and cooperation.

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