The Kra Isthmus in Thailand is the narrowest part of the Malay Peninsula. The western part of the isthmus belongs to Ranong Province and the eastern part to Chumphon Province, both in Southern Thailand. The isthmus is bordered to the west by the Andaman Sea and to the east by the Gulf of Thailand.
The Kra Isthmus marks the boundary between two sections of the mountain chain which runs from Tibet through the Malay peninsula. The southern part is the Phuket Range, which is a continuation of the Tenasserim Hills, extending further northwards for over 400 km (250 mi) beyond the Three Pagodas Pass.
On 8 December 1941 local time, the Imperial Japanese army landed in Songkhla invading Thailand. Because of the International Date Line, this actually occurred hours before the 7 December (Hawaii time) attack on Pearl Harbor, making it the first major action of the Pacific War. The Japanese forces then moved south towards Perlis and Penang as part of the Malayan campaign which culminated in the capture of Singapore.