units of its 15th Army under Lieutenant General Shōjirō Iida and 25th Army under Lieutenant General Tomoyuki Yamashita stationed in Indochina. Both armies had combat aircraft units. The 15th Army was tasked with the attack on Burma and the 25th with Malaya and Singapore. In order to attack Burma, the 15th Army needed to pass over the Bangkok plain, while the 25th Army needed to attack Malaya via the Kra Peninsula. The attack through Thailand on Malaya and Singapore was planned by Colonel Masanobu Tsuji while he was part of Unit 82. The Japanese had about 100,000 troops who needed to pass through Thailand. Naval forces Ships from IJN 2nd Fleet under Admiral Nobutake Kondō provided support and cover for the landings in Thailand and at Kota Baru in Malaya. The known IJN ships participating, apart from those sent to Kota Baru, were: the cruiser IJN Kashii escorted seven transports carrying troops of the 143rd Regiment from Saigon Destroyers Asagiri, Amagiri, Sagiri, Yugiri, Shirakumo, and Shinonome supported the 25th Army landings in southern Thailand Escort ship IJN Shimushu escorted transports Zenyo Maru, Miike Maru and Toho Maru''' to Nakorn Sri Thammarat, southern Thailand, with more of the 143rd Regiment Merchant seaplane carriers Kamikawa Maru, Sagara MaruIn total there were 18 transports involved, which included three landing troops at Kota Baru. Japanese invasion Japanese troops invaded Thailand from Indochina and with landings south of Bangkok and at various points along the Kra Peninsula several hours after Thailand had not responded to their ultimatum. While the government debated a response, Phibun could not be located and was unaware of the ultimatum until late morning. 15th Army objectives Phra Tabong Province At dawn the Imperial Guards Division under Lieutenant-General Takuma Nishimura and IJA 55th Division under Lieutenant-General Hiroshi Takeuchi of the 15th Army crossed the border from Indo-China into Thailand's recently reclaimed Phra Tabong Province at Tambon Savay Donkeo, Athuek Thewadej District (Russei) of Battambang. The Japanese encountered no resistance, and from Sisophon swung north-westwards into Aranyaprathet (then still a district of Prachinburi Province) along the nearly finished railway link between Aranyaprathet and Monkhol Bourei. (It opened for traffic on 11 April 1942.) Chumphon The Japanese 1st Infantry Battalion of the 143rd Infantry Regiment (part of the IJA 55th Division) landed at Chumphon on the morning of 8 December from two troop ships. They managed to form a perimeter around their landing areas,