This was the British advance into southern Thailand just after the Japanese ‘E’ (i) invasion of Malaya (8/11 December 1941).
The operation was named ‘Krohcol’ after the fact that its core was Lieutenant Colonel H. D. Moorhead’s mechanised column, comprising two companies of infantry and the carriers of the 3/16th Punjab Regiment together with a few anti-tank guns and engineers, operating on the road linking Kroh and Patani.
The operation was authorised by Lieutenant General A. E. Percival, commanding the British-led ground forces in Malaya, as a scaled-down ‘Matador’ (i), the plan for a pre-emptive strike into Thailand which had been prohibited by the British government. As a result of delays in authorisation by Percival and in the forwarding of his order, the need to reorganise the troops for ‘Krohcol’ instead of ‘Matador’ (i), and Thai resistance, the 'Krohcol' column did not reach ‘The Ledge’ (see below) in time to achieve its task.
The 'Krohcol' force was the most important of three columns sent into Thailand to harass and delay the Japanese advance from their beach-heads at Singora (now Songkhla) and Patani. Attached to Moorhead’s command were some Australian veterans of World War I from the Australian Reserve Transport Company. The 'Krohcol' force was below its designated strength and delayed by the fact that the 1/8th Punjab and a light artillery battery did not arrive in time, and in fact the column left without them. The objective was a 6-mile (10-km) stretch of road cut through a steep hillside and bounded on the other side by sheer drop into a river and known as ‘The Ledge’. Blowing the hillside onto the road would seriously delay the advance of Lieutenant General Takuro Matsui’s 5th Division, of Lieutenant General Tomoyuki Yamashita’s 25th Army, toward Kroh in the northern part of Malaya.
Opposing this British-led force was the resistance of the Thai gendarmerie, which caused further delays to the column. The 'Krohcol' force crossed the frontier some 14 hours after the landing of the Japanese ‘Takumi’ Force at Kota Bharu on the north-east coast of Malaya, and met stubborn opposition from the Thai gendarmerie and civilian volunteers led by Major Prayoon Rattanakit, police commissioner of the town of Betong.
This force harassed the British column from the safety of the surrounding forests and felled rubber trees across the narrow road, slowing the progress of the British-led column’s tracked carriers. In the meantime much of the Thai population evacuated the town of Betong, leaving behind Chinese and Indian merchants. Thai resistance delayed the Punjabis until the following afternoon, and the 'Krohcol' force did not reach Betong, a mere 5 miles (8 km) inside the frontier, until the evening of 9 December.
It is not known why Moorhead did not immediately push on to ‘The Ledge’, but the delay proved decisive. On the morning of 10 December, the Punjabi troops set off from Betong for ‘The Ledge’. At about 14.00, while advancing through a ravine above the Patani river, they came under fire again: the 'Krohcol' force had now made contact with the 5th Division. Fighting went on into the night, and continued on the following day. With casualties mounting, Moorhead decided to fall back to Betong, and received permission to do so from the headquarters of Major General D. M. Murray-Lyon’s Indian 11th Division.
Nearly outflanked by the Japanese, the 'Krohcol' force began to retreat at dawn on 11 December. That night the local Thai gendarmerie was reinforced by Japanese tanks arriving from the landings at Patani, and the Japanese pressed on to pursue and engage the 'Krohcol' force, which was only 5 miles (8 km) from ‘The Ledge’. A prisoner released from a local jail, an ex-bandit who knew the area well, was borrowed by the Japanese as a guide. Betong was reoccupied, and the force under Prayoon began taking punitive actions against the local Chinese, who were believed to have welcomed the arrival of the 'Krohcol' force.
Moorhead was forced to make a fighting retreat back to Kroh, where his missing battalion was digging in.
One of the other columns, consisting of 200 lorried troops from the 1/18th Punjab, and a section of the 273rd Anti-Tank Battery, had crossed the Malay/Thai border farther to the west than the 'Krohcol' force but at the same time. Named Laycol after Brigadier W. Lay, commander of the Indian 6th Brigade, the column crossed the frontier at 17.30 on 8 December and moved north, along the road linking Changlun in Malaya and Singora in Thailand, to harass and delay the Japanese. Laycol reached Ban Sadao, 10 miles (16 km) to the north of the frontier, at dusk and halted to take up a position north of the village. It was here that Laycol made contact with a Japanese mechanised column from Colonel Saeki’s 5th Reconnaissance Regiment of the 5th Division. The Japanese force was led by tanks and moved in close formation with full headlights. The two leading tanks were knocked out by the anti-tank guns, but the Japanese infantry quickly debussed and started an enveloping movement around the Punjabis' flanks.
Laycol withdrew on 11 December through the outpost position at Kampong Imam, destroying two bridges and partially destroying a third on the way back.
The last column associated with the ‘Krohcol’ force and its operation was an armoured train, carrying a 30-man detachment of the 2/16th Punjab and some engineers, and this advanced into Thailand from Padang Besar in the Perlis area of northern Malaya. The train reached Khlong Ngae in Thailand and its attached party destroyed a 200-ft (60-m) bridge before withdrawing to Padang Besar.