The 'Battle of the Slim River' was fought between Japanese and British-led Indian forces during the Malayan campaign in January 1942 on the western coast of Malaya (7 January 1942).

Japanese forces had invaded north-west Malaya from southern Thailand in the 'E' (ii) operation on 11 December 1941 and eastern Malaya on 7 December at Kota Bharu. From Thailand the Japanese had driven relentlessly to the south along Malaya’s western coast, defeating all British attempts at stopping them. By 25 December the Japanese held all north-western Malaya. One of the few moments where British troops managed to create any form of effective defence against the Japanese tactics occurred near Kampar on the Dipang river: in the 'Battle of Kampar', a four-day battle notable for the effectiveness of the British artillery, the Japanese suffered heavy casualties. By 2 January 1942, however, Brigadier A. C. M. Paris’s Indian 11^th Division had been outflanked by Japanese seaborne landings to the south of the Kampar position, was outnumbered and was faced by Japanese forces attempting to isolate the division from the road to Singapore. The division then withdrew to prepared positions at Trolak, some 5 miles (8 km) to the north of the Slim river.

The defences on the road to Trolak started with a 4-mile (6.4-km) corridor at the 60-mile (96.6-km) post extending through almost impenetrable jungle to the 64-mile (103-km) post. After the village the road cut through the more open terrain of the Cluny rubber estate for 5 miles (8 km) before reaching the railway bridge over the Slim river. The road then bent to the east and followed the river upstream for another 6 miles (9.7 km) before crossing the Slim river at a road bridge. The British commander, Acting Major General Paris (normally commander of the Indian 12^th Brigade), had lost one of his three brigades after the fighting at Kampar: the amalgamated Indian 5^th/16^th Brigade, after retreating through the Indian 12^th Brigade, had been moved to a coastal defence position farther to the south to defend the division’s western flank and to rest and reorganise. This left Paris with Lieutenant Colonel Ian Stewart’s Indian 12^th Brigade and Lieutenant Colonel Ray Selby’s Indian 28^th Brigade, both at reduced strengths as a result of the heavy casualties they had sustained in the earlier 'Battle of Kampar' and the fighting on the Grik Road, to defend the river’s northern bank.

Stewart’s battalions were in a line straddling each side of the road and spreading back through the thick jungle part of the corridor to the north of Trolak, where the Cluny rubber estate started and where Stewart located his Headquarters. The 4/19^th Hyderabad Regiment held the forward position with anti-tank obstacles and roadblocks. The next and last prepared positions were held by the 5/2^nd Punjab Regiment. The 2^nd Argyll and Sutherland Highlanders were grouped in a defensive position but without fixed anti-tank obstacles or roadblocks. Selby’s Gurkha infantrymen were spread along the road and railway leading up to both bridges, which had been readied for demolition.

The Japanese attacking force was drawn from Colonel Ando’s battle group (mainly of the 42^nd Regiment) which had taken over from the chastened 'Okabe' Detachment (41^st Regiment) which had suffered heavy casualties in the artillery ambush at Kampar. Both these units were of Lieutenant General Takuro Matsui’s 5^th Division. The assault force comprised some 17 Type 97 Chi-Ha medium tanks and three Type 95 Ha-Go light tanks under the command of Major Toyosaku Shimada, who developed the plan, unusual for World War II, of a night attack using tanks to spearhead the infantry. This was a dangerous proposition for tanks considering these vehicles' very limited fields of vision, a factor which would greatly hamper their crews.

On the afternoon of 5 January, the Indian 5^th/16^th Brigade’s rearguard withdrew through the Indian 12^th Brigade’s positions. Soon after this, the advance guard of the 42^nd Regiment reached the positions of the 4/19^th Hyderabad Regiment’s positions and launched a probing attack that was beaten off with the loss of 60 Japanese dead. Ando decided to hold and wait for armour support before launching another attack. On 6 January Shimada’s tank company arrived and Shimada begged Ando to allow him to attack straight down the road rather than follow the usual Japanese tactics of flanking the British positions.

At 03.30 on 7 January, in heavy rain, Shimada’s force started a mortar and artillery bombardment of the first of the British positions (occupied by the 4/19^th Hyderabad Regiment under Major Alan Davidson Brown as the battalion’s commanding officer, Lieutenant Colonel Eric Wilson-Haffenden, had been wounded in an air attack. The tanks began to manoeuvre through the British defensive obstacles under fire from the Hyderabads, who were able to call in some artillery fire that destroyed one tank. The Hyderabads then lost contact with their artillery support and, without any anti-tank weapons to defend against the Japanese tanks, could not prevent the 3/42^nd Regiment from forcing a breach in their roadblock. Within 15 minutes, Japanese engineers were dismantling the road block and Ando’s infantry was pushing back the Hyderabads, now reduced to scattered groups. The Japanese infantry were immediately followed by Shimada’s tanks, which easily broke through the remaining Hyderabads, scattering them into the jungle, and by 04.00 were headed toward the next British unit.

A few Hyderabads fell back to the next battalion, which was Lieutenant Colonel Charles Cecil Deakin’s 5/2^nd Punjab Regiment, alerting the Punjabis to the tanks heading toward their position. Shimada lost his two leading tanks to land mines and Boys anti-tank rifle fire in front of the position held by the more experienced Punjabis, who then managed to set fire to another tank with Molotov cocktails, effectively blocking the road and leaving the Japanese column stacked up, almost bumper to bumper: if the British artillery, which was not contacted as a result of the severing of the communication lines, had been been called in at this point in the battle, Shimada’s column could have been easily stopped in a vulnerable position, surrounded by thick jungle on a narrow road. This golden opportunity for the British was lost and Shimada’s infantry were able to push through Deakin’s Punjabis, while the tanks found an unguarded loop road that enabled them to bypass the destroyed tanks. The Punjabis had held Shimada until around 06.00 in heavy fighting. Deakin and a handful of his remaining Punjabis managed to escape across the Slim river, but most of the battalion’s men were mopped up by the 42^nd Regiment.

By 06.30, Shimada’s tanks were approaching the next battalion, the 2/Argyll and Sutherland Highlanders under the command of Lieutenant Colonel Lindsay Robertson. The 2/Argylls were positioned around the village of Trolak itself and protected the headquarters of Stewart’s Indian 12^th Brigade. The Argylls were a regular British battalion and very experienced, considered to be one of the best jungle fighting units the British had in Malaya. The Argylls were in a defensive position but without fixed anti-tank obstacles or mines. They received but scant warning of the rapidly approaching Japanese, thanks to the arrival of a few panic-stricken Hyderabads to erect a roadblock. Even with that warning, the first four of Shimada’s tanks were mistaken for Punjab Bren Gun Carriers and drove straight through the Argylls, neatly dividing the battalion, and then headed for the railway bridge. The arrival of the remainder of Shimada’s main force and then Ando’s infantry split the Argylls completely and isolated them from the road. The Argylls were reduced to many small groups, but these fought ferociously and managed to delay the Japanese infantry longer than either of the other two battalions, holding them until about 07.30. The force to the east of the road (C and B Companies) under Robertson fought their way into the rubber estate and tried to flank the Japanese advance by heading to the south through the jungle inland and dividing into small parties. Six weeks later some of these soldiers were still in the jungle. A Company, commanded by Lieutenant Donald Napier, to the west of the road, managed to break out of the encircling Japanese and cross the river before the railway bridge was blown. D Company, farther to the north than A Company, suffered the same fate as Robertson’s party, having to scatter into the jungle and attempt to regain the British lines. Most of D Company was captured before the men could reach the river, and only 94 Argylls answered roll call on 8 January, nearly all of them men of Napier’s A Company.

A Japanese atrocity was committed in the area of the rubber trees around Trolak, an area in which were a number of Argyll and Hyderabad wounded. 2^nd Lieutenant Ian Primrose reported that after he regained consciousness from an injury during the fighting he discovered that the Japanese were dividing the wounded into those who said they could walk and those who said they could not. Primrose decided he could walk, which was fortunate as the Japanese proceeded to shoot and bayonet the wounded who could not. Afterward the survivors were forced to dig graves for the dead and then told to carry the Japanese wounded.

Before reaching the Indian 28^th Brigade, Shimada’s tanks were offered a perfect target in the form of Lieutenant Colonel Cyril Livesy Lawrence Stokes’s 5/14^th Punjabs, who were in marching order on each side of the road to Trolak. Stokes’s Punjabis were moving to reinforce Stewart’s brigade. Commanding Shimada’s three leading tanks was Lieutenant Sadanobu Watanabe, who now led his tanks straight through Stokes' Punjabis, machine guns firing at the perfect target offered by the columns of men. Stokes was injured on 7 January when he and Major Lewis were attacked by tanks when advancing to the front, and Stokes died in captivity on 15 February. His battalion suffered heavy casualties before Watanabe’s tanks carried on toward the road bridge: the 5/14^th Punjab Regiment mustered a mere 146 officers and soldiers by 8 January. By 08.00, the leading Japanese tanks were within the area of Selby’s brigade headquarters. The Indian 28^th Brigade was completely unaware of what had happened to Stewart’s brigade and the Japanese tore through them faster, scattering both the 2/2^nd and 2/9^th Gurkha Regiments, which were spread around Selby’s headquarters. Although they suffered heavy casualties, many of the soldiers from these two battalions made it across the railway bridge before the main Japanese force reached their position.

Like the Punjabis, the last battalion of Selby’s brigade, the 2/1^st Gurkhas under the command of Lieutenant Colonel Jack Oswald Fulton, was on the march on each side of the road as the Japanese tanks reached it. On this occasion, however, the marching column of Gurkhas was facing away from the approaching Japanese, and Watanabe’s tanks caught them from behind: the death toll was even higher than that of the Punjabis: only one officer and 27 men answered roll call on the next day. Fulton, wounded in the stomach and taken prisoner, died in captivity two months later.

By this time, Shimada’s tanks had broken through both brigades and were into the Indian 11^th Divisin’s rear area and heading for the two bridges. Leaving the railway bridge for Shimada and the main Japanese force, Watanabe headed toward the more important road bridge 6 miles (9.7 km) away. In this attack Watanabe broke through the artillery, medical and other support units in front of the road bridge. Two British artillery colonels were surprised and killed while driving on the road. On reaching the road bridge at 08.30, Watanabe found it defended by a battery of 40-mm Bofors anti-aircraft guns of the Singapore and Hong Kong Artillery Regiment. Although two of the guns managed to lower their barrels quickly enough to engage the tanks, the rounds did not damage the tanks' armour and the gunners then fled. Watanabe himself cut the wires to the demolition charges on the bridge with his sword. It was still only early in the morning and the Japanese attack had managed to scatter the entire Indian 11^th Division, leaving most of its survivors attempting to escape across the Slim river.

In the last part of this 16-mile (25.75-km) high-speed attack, Watanabe, now in control of the road bridge, sent a force of three tanks under the command of Ensign Toichero Sato to explore the other side of the river. Sato travelled 2.5 miles (4 km) before encountering more British artillery, in the form of two 4.5-in (114.3-mm) howitzers of the 155^th Field Artillery Regiment. Sato’s tank opened fire on the first gun, turning it over and blocking the road. The gunners of the second gun managed to lower their barrel in time to fire on the tanks at pointblank range. Sato’s tank was hit and destroyed, killing him, and forcing the other two tanks to fall back to the road bridge.

The Indian 11^th Division had suffered major losses, although some errant men eventually made their way back to rejoin in the fight for Singapore. Many more remained in the jungle after the surrender, and large numbers of these survivors were later taken prisoner, while a few, such as Lieutenant Colonel Lindsay Robertson, who had strong views about surrendering, and his party of Argylls attempted to evade capture, but were unable to keep ahead of the rapid Japanese advance. Robertson was killed on 20 January. The two brigades' remaining survivors were scattered all over the Malayan peninsula, and some Argylls were still at large at the time of the Japanese surrender in August 1945. A Gurkha non-commissioned officer, Naik Nakam Gurung, was found during the Malayan Emergency in October 1949 after living in the jungle since 1942.The Indian 12^th Brigade had effectively ceased to exist and the Indian 28^th Brigade was but a shadow of its original self.

Stewart’s Indian 12^th Brigade could muster no more than 430 officers and men, with 94 officers and men of the Argylls. Selby’s brigade was slightly better off with 750 answering roll call the next day. In all the Indian 11^th Division lost an estimated 3,200 men and a large quantities of irreplaceable equipment. The Japanese had managed to attack through a division along 19 miles (30.6 km) and take two bridges at minimal cost to themselves. After meeting survivors of the battle, General Sir Archibald Wavell, the commander-in-chief in India, was appalled by their condition in and ordered the Indian 11^th Division out of the front line. This British defeat allowed the Japanese to take Kuala Lumpur unopposed: Wavell had ordered Lieutenant General A. E. Percival, the commander in Malaya, to retreat into southern Malaya, giving up central Malaya, and then to allow Major General H. G. Bennett’s Australian 8^th Division an opportunity to prove itself against the Imperial Japanese army.

The devastation caused by this short battle also resulted in Percival changing his tactics of prepared defensive positions and ordering a rapid retreat to the south, where an ambush was to be prepared by the Australians at Gemensah bridge.