Battle of Slater's Knoll

At the beginning of 1945, the south-eastern part of Bougainville was occupied by the Japanese 6th Division,[2] under the command of Lieutenant General Tsutomu Akinaga.[Note 1] Made up of the 13th and 23rd Infantry Regiments—600 and 700-strong respectively—as well as the 6th Field Artillery Regiment, the 6th Engineer Regiment, the 6th Transport Regiment and the 4th Field Heavy Artillery Regiment, Akinaga's division consisted of 3,300 men.[4][5][Note 2]

The previous November, the Australian II Corps under Lieutenant General Stanley Savige had taken over responsibility of the island from the US XIV Corps, who had been transferred to fight in the Philippines. Although incorrect, at the time the Allies believed that the Japanese forces on the island numbered around 17,500 men[6][Note 3] and while these forces were understrength, they were still considered to be capable of carrying out effective combat operations. In order to counter this, it was decided that the Australian II Corps—consisting of Militia and Australian Imperial Force troops from the 3rd Division and the 11th and 23rd Brigades[8][Note 4]—would go on the offensive[10] and a three-pronged campaign was planned in the northern, central and southern sectors of the island.[11][12]

As a result, the Australian campaign on the island developed into three separate drives: in the north, it was planned that Japanese forces would be forced into the narrow Bonis Peninsula and contained; in the centre, the seizure of Pearl Ridge would give the Australians control of the east–west thoroughfares and protection against further counterattacks, while also opening the way for a drive to the east coast; and the main campaign would take place in the south, where the bulk of the Japanese forces were concentrated.[11] Consequently, on 21 January, Savige directed the 3rd Division under Major General William Bridgeford to take "swift and vigorous action" to destroy Japanese forces in southern Bougainville. The division's immediate task was to advance south to the Puriata,[Note 5] and send patrols across it. Savige considered that the Japanese division was "weak and off balance"[14] due to casualties and disease as well as a shortage of supplies. Brigadier Raymond Monaghan's 29th Brigade had opened the campaign in the south in mid-December, crossing the Jaba River, before conducting a series of landings by barge along the coast of Empress Augusta Bay, outflanking the Tuju, Tavera, Adele and Hupai Rivers, in what became dubbed the "Battle of the Swamps" by the Australians. The fighting during this time resulted in 240 Japanese killed, and 148 Australian casualties. Monaghan was also relieved of his command.[15]

In late January, the 7th Brigade, under Brigadier John Field, which had been patrolling the Jaba River to protect the 29th Brigade's rear while they pushed south, was subsequently tasked to "take Mosigetta, clear the enemy from the Kupon–Nigitan–Sisiruai area, and patrol along the Puriata".[16] Each of the brigade's three infantry battalions was marginally below full strength at the time, with frontages of between 600 and 700 personnel around the start of the battle.[17][18][19]

In late January, a company from the Australian 25th Infantry Battalion—under Lieutenant Colonel John McKinna—subsequently carried out an amphibious landing south of Motupena Point, on the Solomon Sea coast and had cleared towards Matsunkei. On 2 February, the battalion carried out another landing at Toko, and advanced northeast from there towards Batara, and then along the west bank of the Puriata, towards the Buin Road.[20][Note 6] Meanwhile, further to the east, the 9th Infantry Battalion was moved by truck from Torokina to the Jaba River and then moved by barge along the Empress Augusta Bay coast, landing at Mawaraka from where they advanced towards Mosigetta, and the 61st Infantry Battalion also proceeded towards there, setting off from the junction of the Jaba and Pagana Rivers while the 2/8th Commando Squadron provided flank security further to the east.[20] Elements of the 1st New Guinea Infantry Battalion also conducted a landing on the coast, on the 25th Battalion's left flank, to the north of Toko, and advanced to Makaku and then towards Mosigetta.[22]

Men from the 61st Infantry Battalion patrol along the Mosigetta River on Bougainville in March 1945 in the lead up to the Battle of Slater's Knoll.

On 4 March, a company from the 25th Infantry Battalion crossed the Puriata River southward—at the point where the Buin Road crossed—on a north-facing bend, later known as Galvin's Crossing.[23] The following day the Japanese were forced off a small knoll close to the river and the road, about 1 km (0.62 mi) south of the crossing. On 6 March, Japanese shelling of the knoll wounded an Australian, Private Carl Slater, who held his post until relieved. He was the only casualty during this period, and the knoll was named after him.[23][Note 7] Throughout March, the 25th Infantry Battalion continued to expand its perimeter, to the north and south, along the Buin Road, while the 9th moved west from Mosigetta to link up with them and the 61st skirted east around Makapeka.[20] By late March, though, heavy rain temporarily stopped the Australian advance, as the main road became impassable due to thick mud.[25]

Although the Japanese sporadically shelled the knoll during March, there were no further Australian casualties. The 25th Infantry Battalion, which had established its headquarters and main defensive position around the knoll, in front of the Puriata River, sent out patrols every day, and on 9 March, one of these reported having killed 10 Japanese soldiers without loss to itself.[23] The Japanese also began making dawn attacks, in which light machine gunners would approach by stealth, set up and fire on the Australian positions, then retire to their own lines, 250 yd (230 m) away. As the advance was halted, the Australians began to expect a major attack in the area of the knoll.[26][27]

The Japanese launched a number of attacks on the Australians between 15 and 17 March.[26] Under fire from three sides and in danger of being enveloped, on 19 March the Australians launched an attack of their own along the Buin Road, and although they had some success in clearing the forward Japanese positions, they then encountered a system of pillboxes and trenches around the Hatai Road junction.[28] The 25th Infantry Battalion's commander, McKinna, ordered the two platoons led by Lieutenant Dick Jefferies to attack the pillboxes, supported by a section of machine guns, and several PIAT anti-tank weapons. A two-hour fire-fight and a bayonet charge followed.[29] This attack was ultimately beaten back by the defenders with the loss of eight Australians killed and 14 wounded.[27][30] A second attack was launched on 22 March. Supported by heavy artillery, mortars and machine guns, it proved successful, largely after the individual efforts of Corporal Reg Rattey, who single-handedly silenced several bunkers.[31][27]

As the Australians began to prepare for the next stage of the offensive,[32] important intelligence confirmed that the Japanese were planning a large-scale counterattack in the area.[33] Believing that the Australian forces in the area surrounding the knoll were limited to just 400 men and observing that the Australians had not had time to reorganise, the Japanese XVII Army commander—Lieutenant General Masatane Kanda—ordered the 6th Division commander—Akinaga—to delay the Australian advance towards the south. Akinaga assessed that a counterattack against the Australian forces at this point with the entire weight of his division might be successful at this time and consequently he gave the order for his division to begin an attack across the Puriata.[5][34] Akinaga planned to commit 2,000 men to the assault, while 1,300 would be held back to act as ammunition carriers.[24]

According to Karl James, no detailed orders were produced for the attack and deliberate planning was hastily completed with little or no co-ordination between the attacking infantry regiments. In addition, to increase the size of the infantry force, troops from the field artillery regiment were quickly re-roled as riflemen.[24] In the meantime, the Australians on Slater's Knoll, having been alerted to the possibility of a large-scale attack, began adjusting their defences. The soldiers cleared fields of fire and set out clear engagement areas to the north, northwest and south of the knoll, to allow maximum effectiveness of their supporting Vickers medium machine guns and Bren light machine guns. Barbed wire was laid out, and booby traps set.[35]

The day after the final Japanese assault on the knoll, 292 dead Japanese were counted around 'B' Company's perimeter.[46][47] In total, over the course of the battle, the Australians counted 620 Japanese killed, and estimated that another 1,000 had probably been wounded.[48] Information obtained from captured Japanese clarified that the Australians had come up against a force of at least 2,400 troops.[49] The commander of the 23rd Infantry Regiment, Lieutenant Colonel Kawano Koji, was among the dead, as was a senior divisional staff officer, Lieutenant Colonel Honda Matsuo.[50] Four wounded Japanese were also taken prisoner of war. Casualties for the Australians included 10 officers and 179 other ranks killed or wounded, while there had been a further 81 Australians evacuated due to non-combat related issues.[51] Wartime Japanese casualty estimates vary from these figures, though, claiming to have killed 1,800 Australians, while placing their own losses at 280 killed and 320 wounded. Long argues that these figures are problematic, as based upon the same report, the Japanese believed that there were only 400 Australians in the region during the battle, and yet they claimed to have killed almost five times that number.[5]

Japanese killed during the final assault on Slater's Knoll are buried the day after the battle

The result of the battle had a profound effect on the Japanese commanders. According to James, Kanda had been "so certain of victory...[he]...had not developed any plans for...subsequent activities".[52] After the battle, the Japanese forces in the area pulled back to the Hongorai River, where they were reorganised due to the heavy losses, with several infantry, engineer and artillery units being amalgamated. Lacking food, suffering the effects of disease, and isolated from home, morale amongst the Japanese troops fell heavily, with many realising that the war was lost. There was an increase in desertions at this time, although the vast majority continued to fight, if only because they were under orders to do so.[53]

Operationally, the battle proved to the Australian high command how effective armour could be when used in close co-operation with infantry and in protecting the lines of communication.[5] The use of machine gun carriers to carry out the wounded had also been quite effective.[49] While the Japanese soldiers and officers on the ground fought bravely, continuing the assault even when it was clear it had failed, ultimately the battle proved to be a decisive Australian victory; however, James notes that poor planning and unreliable communications had also contributed to the result.[54] Long goes on to argue that if the Japanese commander had been more flexible in his tactics, the result might have been different. The Australian right flank had been vulnerable, but Akinaga did not exploit this opportunity.[5]

There were tactical deficiencies as well, particularly the predictability of cutting Australian signals lines just before an attack and bunching together in tight groups during an assault, allowing the Australians to take full toll with their machine guns. The Australian commander of the 25th Infantry Battalion, McKinna, had spread his companies out effectively and went forward to direct the fighting at several points. Fields of fire had been cleared, perimeters set and patrolling had been maintained.[55] Nevertheless, the Australians had also failed to seize opportunities as they arose, for after the battle they did not follow up their success immediately. After the failure of the final assault, the Japanese had possessed no forces in the immediate vicinity that would have been capable of resisting any follow up forces that the Australians might have been able to bring up, and it is possible that an advance could have been carried all the way to the Hongorai River. As it was, however, the Australian line of supply was stretched and it was necessary for a pause before the advance could continue in earnest.[56]

In the days immediately after the battle, the Australians continued to carry out patrolling operations around the knoll. On 7 April, a patrol from the 9th Infantry Battalion clashed with a Japanese force of about 30 men and in the ensuing engagement four Japanese were killed, while a patrol from the 61st Infantry Battalion on 8 April killed another five. On 13 April, the order was given that the 7th Brigade would be gradually withdrawn and relieved by the 15th.[57][58] Shortly afterwards, the 58th/59th Infantry Battalion replaced the 25th in occupation of the knoll, while the 24th Infantry Battalion resumed the advance along the Buin Road on 17 April,[59] subsequently taking part in the fighting along the Hongorai River.[60] The 9th Infantry Battalion, however, was not withdrawn immediately, and remained in the northern area until it handed over to the 57th/60th Infantry Battalion in early May. The fighting on Bougainville continued throughout April as the Japanese resisted the Australian advance and went on until July when the fighting petered out due to heavy rain and flooding.[61]

After the war, the battle honour of "Slater's Knoll" was awarded to the 25th Infantry Battalion and the 2/4th Armoured Regiment. Neither the 9th or 61st Infantry Battalions were similarly credited, although according to Gordon Maitland there seems to be no explanation as to why.[62] For his actions during the attack on the Japanese pillboxes on 22 March, Rattey later received the Victoria Cross. Initially, his battalion commander, McKinna, had nominated him for the lesser Distinguished Conduct Medal, but on review by Field, the brigade commander, the nomination was elevated. It was subsequently announced in the London Gazette in July 1945.[63][64]