Battle of Tsimba Ridge
Encyclopedia
The Battle of Tsimba Ridge was a battle of the Second World War involving Australia
n and Japan
ese forces. Part of the wider Bougainville Campaign of the Pacific theatre
, the battle occurred in the northern sector of Bougainville Island
between 17 January and 9 February 1945, when the lead battalion of the Australian 11th Brigade
—the 31st/51st Battalion
—advanced towards the Genga River as they drove towards the Bonis Peninsula. Coming up against heavy resistance along Tsimba Ridge, the Australian advance was halted for three weeks as they fought to wrest control of the ridge from the Japanese defenders. The main Australian attack came on 6 February, however, it was not until 9 February when the Japanese completely withdrew from the position. Nevertheless, fighting in the surrounding area continued until 22 February.
took over responsibility for Allied operations on Bougainville from the American XIV Corps. Mistakenly believing that the Japanese forces on the island numbered just 17,500 men it was decided that the Australians would pursue an aggressive campaign to clear the Japanese from Bougainville. The campaign 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 avenues of approach, as well as affording them protection against further counter-attack
s, while also opening the way for a drive to the east coast; and the main campaign in the south, where the bulk of the Japanese forces were concentrated. Allied estimates of Japanese strength were later found to be grossly inaccurate and after the war it was found that the number of Japanese alive on the island at this time was closer to 40,000.
to begin clearing operations along the northeast coast of the island towards Soraken Harbour
, as they attempted to drive the Japanese in the sector on to the narrow Bonis Peninsula. At the time the Australians believed there to be around 390 Japanese defending the area surrounding the Genga River—considered to be the main Japanese defence line in the northern sector—however, it was later determined to be closer to 900 men from the 81st Infantry Regiment, under the command of Lieutenant Colonel Shinzo Nakamura. Nakamura, who was considered to be a "master of jungle warfare", had been ordered to prevent the Australian advance along the coast, but had perceived the likelihood of stopping them before the Genga as being unlikely and had as such decided that he would concentrate his defence around Tsimba Ridge, with supporting elements being placed to the north, near Kunamatoro.
Taking over control of the northern sector from the 7th Brigade, which was subsequently transferred to southern sector to take part in the main offensive, the 11th Brigade advanced along the coast from Kuraio Mission, sending out patrols into the interior to flush the Japanese out of their positions in the mountains as they went. The 31st/51st Battalion
, under the command of Lieutenant Colonel Joseph Kelly formed the vanguard
of the advance, its main body moving along the coast road towards Amun
, Sipaai and Rukussia, while patrols were sent inland from Totokei towards Lalum and Soraken
, both of which were considered key Japanese positions. By 16 January the lead company of the 31st/51st reached Rukussia, having encountered no Japanese up until that point.
-sized patrol came across a number of huts in a cleared area and proceeded to launch an attack on it. One Japanese was killed in the initial attack, however, as the Australians took the huts and pushed forward beyond them, they were engaged from entrenchments 100 yards (91.4 m) in front of them. The Japanese then proceeded to launch a counter-attack using light and heavy machine guns. In response, the Australians brought up another platoon and over the course of two days the counter-attack was repulsed, with six to eight Japanese estimated to have been killed and a number wounded, while two Australians were wounded.
During the engagement the Japanese had opened up with the artillery
that they had brought up in support of the main defensive position on Tsimba Ridge, firing for the first time in the sector; this barrage, however, proved largely ineffective, inflicting only one casualty, as many of the shells proved to be faulty and did not detonate. The Australians also came across large camp, including a field hospital, which they captured intact, while another group of huts was discovered, from where they gained intelligence identifying the Japanese troops in the area as belonging to the 81st Infantry Regiment. They also managed to capture two 70 mm guns, and a quantity of ammunition for them.
On 19 January the 31st/51st Battalion's 'A' Company sent a patrol out to outflank
the Japanese forward positions; this patrol moved first to the right flank and then headed north along the tracks around Totokei and Goton. Discovering evidence of Japanese movement in the area, they followed these to the village of Kunamatoro, about 1 miles (1.6 km) north of Junapopo. Here they encountered a force of around 30 to 50 Japanese and after the initial contact, in which the Australian platoon commander was wounded, the patrol attacked the village. Within 10 minutes the battle was over: 14 Japanese had been killed, along with a further five wounded, while the Australians suffered one killed, one wounded and one missing. As darkness fell, the Australian patrol withdrew from the village.
The following day—20 January—the advanced elements of the Australian force pressed on towards Tsimba Ridge. A formation about 200 yards (182.9 m) long and about 60 feet (18.3 m) in height, and stretching westerly to the Genga River where a steep cliff
fell to the southern bank of the river, the ridge blocked the Australian advance across the river, while its south-eastern most protrusion (later known as 'the Pimple') was separated by a shallow saddle. On top of the ridge, dense jungle provided good concealment
, while the approaches to the ridge were largely open to observation. As the Australians approached the ridge, one of their platoons captured a 47 mm gun which had been positioned along the coast about 1000 yards (914.4 m) south of the ridge, while another platoon contacted a lone Japanese soldier, who was killed in the subsequent fire fight as they entered a garden that curved along the southern approach to the ridge, and which became known as 'the amphitheatre'. After the initial contact, the platoon's advance through the garden was prevented by an intense burst of fire from the ridge, however, the Australians proceeded to scale the high ground that rose to their east and subsequently they were able to occupy the south-eastern tip of the Pimple, capturing two 75 mm guns in the process.
Reports had been received from locals that the Japanese had brought reinforcements down from Soraken, Taiof Island and Tarlena and at this point the Australians realised that the Japanese had concentrated in far greater numbers than anticipated and had in fact established their line of resistance
in the sector upon the ridge. This was confirmed later after the Australians moved forward once more on 21 January, moving to within 800 yards (731.5 m) from the Genga River, where the track upon which they were advancing opened into a large garden, which curved around the edge of Tsimba Ridge, from where the Japanese defenders had an excellent line of sight. Subsequent patrols determined the extent of the Japanese position, reporting that they had constructed a well fortified position with a continuous trench along the crest of ridge, weapons pits and pill boxes, all with clear fields of fire, stretching up to 150 yards (137.2 m).
The Australian commander, Kelly, ordered 'B' Company to move up and take the ridge and over the course of a week between 21–28 January they made a number of attempts. These proved fruitless, however, although one platoon managed to encircle the position from the north before being engaged with heavy machine gun
fire. On 23 January, the Australians established fire support in the form of guns from the 2nd Mountain Battery
. Another three unsuccessful attempts were made on 24 January, while on 25 January 'C' Company carried out a movement to the flank in an attempt to get around behind the ridge and attack from the north. Crossing the crocodile
-infested waters of the Genga about 600 yards (548.6 m) from the ridge, the Australians established a bridgehead
across the river with a line of communication
s back to the Pimple, which they kept open by maintaining a constant patrol along it.
Over the following six days, the Japanese proceeded to attack the bridgehead, launching a number of attacks that bordered upon suicidal. These attacks were repulsed, however, and the Australians began to launch patrols in all directions around the ridge. On 29 January the Japanese launched a large scale attack on 'C' Company's positions and although the Australians resisted stubbornly, the attack succeeded in breaking through one part of the perimeter and managed to roll up the position all the way to the main battalion position around Puto before it was turned back. The Australian counter-attack, organised by the 'C' Company's commander, Captain Alwyn Shilton, and supported by accurate artillery fire, came on 1 February and resulted in over 30 Japanese killed or wounded.
For the next few days further probes were made by the Japanese, however, these were also repulsed and the Australians consolidated their positions in preparation for an assault on the ridge. Preparations at this time included the manhandling of a mountain gun from Puto to a position 150 yards (137.2 m) from the Pimple, from where it could fire directly upon the Japanese positions on the ridge, while aircraft from No. 5 Squadron, Royal Australian Air Force
carried out reconnaisance. In order to maintain the secrecy of these preparations, mortar
fire was brought down upon the Japanese positions to mask the sounds of digging and movement while machine gun fire from Vickers machine gun
s kept the Japanese defenders from being able to leave their shelter and observe.
The attack finally came on 6 February. Supported by a barrage of over 500 artillery shells and mortar bombs, three platoons from 'B' Company assaulted the ridge from different points in an effort to encircle the defenders. Following the artillery preparation fire, the attack began at 0900 hours when two platoons—10 and 11 Platoons—along with company headquarters formed up south-east of the amphitheatre and began to advance to the north-west 200 yards (182.9 m) to attack the ridge from behind, while another force—12 Platoon—attacked from the garden, moving around the Pimple before assaulting the ridge from east.
From the north-west, 10 Platoon, in the centre, managed to capture its objectives by 0925 hours, however, 12 Platoon, came under intense fire and after suffering several casualties stopped their advance. By 1130 hours the most northern Australian platoon, 11 Platoon, had reached the high ground on the north-western side of the ridge, completing the encirclement of the Japanese, however, the defenders refused to give up the position. The attack cost the Australians nine killed and 20 wounded. The next day the Japanese launched a counter-attack which, although repulsed, enabled them to continue to maintain a small pocket of resistance on the western tip of the ridge; this was finally abandoned on 9 February, however, when an airstrike
was called in upon the position and the Japanese withdrew from the feature.
After the fall of Tsimba Ridge, fighting continued around the Genga River for the next couple of weeks. On 10 February area south the Genga had been cleared of Japanese and the Australians began to patrol along the northern bank. A number of minor clashes occurred, the most serious of which saw three Japanese killed and three Australians wounded in an action in which the Australians managed to capture a Japanese 37 mm gun. As the Japanese were forced to withdraw from a position along the track which ran 150 yards (137.2 m) from the river, the Japanese artillery intensified and a number of men from the 31st/51st Battalion became casualties.
The 31st/51st Battalion continued operations around the Genga River until 22 February, when they were relieved by the 26th Battalion, who continued the advance north towards Ratsua
. In total, the Australians lost 34 killed and 91 wounded in the fighting around the Genga River, while it was estimated that the Japanese lost 148 killed.
For their involvement in taking Tsimba Ridge, the 31st/51st Battalion were awarded the battle honour
"Tsimba Ridge".
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
n and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
ese forces. Part of the wider Bougainville Campaign of the Pacific theatre
Pacific War
The Pacific War, also sometimes called the Asia-Pacific War refers broadly to the parts of World War II that took place in the Pacific Ocean, its islands, and in East Asia, then called the Far East...
, the battle occurred in the northern sector of Bougainville Island
Bougainville Island
Bougainville Island is the main island of the Autonomous Region of Bougainville of Papua New Guinea. This region is also known as Bougainville Province or the North Solomons. The population of the province is 175,160 , which includes the adjacent island of Buka and assorted outlying islands...
between 17 January and 9 February 1945, when the lead battalion of the Australian 11th Brigade
11th Brigade (Australia)
The Australian 11th Brigade is an Australian Army brigade which currently comprises most Australian Army Reserve units located in Queensland. The Brigade was first formed in early 1916 as part of the 3rd Division and saw action during World War I and World War II.-Brigade Structure:*Headquarters...
—the 31st/51st Battalion
31st/51st Battalion (Australia)
The 31st/51st Battalion was an infantry battalion of the Australian Army, which served during World War II. Raised for service as part of the Militia in 1943 through the amalgamation of two previously existing battalions, the 31st/51st Battalion undertook garrison duties in Dutch New Guinea in...
—advanced towards the Genga River as they drove towards the Bonis Peninsula. Coming up against heavy resistance along Tsimba Ridge, the Australian advance was halted for three weeks as they fought to wrest control of the ridge from the Japanese defenders. The main Australian attack came on 6 February, however, it was not until 9 February when the Japanese completely withdrew from the position. Nevertheless, fighting in the surrounding area continued until 22 February.
Background
In November–December 1944, the Australian II Corps under Lieutenant General Stanley SavigeStanley Savige
Lieutenant General Sir Stanley George Savige, KBE, CB, DSO, MC, ED , was an Australian Army soldier and officer who served in World War I and World War II, rising to the rank of lieutenant general....
took over responsibility for Allied operations on Bougainville from the American XIV Corps. Mistakenly believing that the Japanese forces on the island numbered just 17,500 men it was decided that the Australians would pursue an aggressive campaign to clear the Japanese from Bougainville. The campaign developed into three separate drives: in the north, it was planned that Japanese forces would be forced into the narrow Bonis Peninsula
Bonis Peninsula
The Bonis Peninsula is a narrow peninsula located on Bougainville Island, Papua New Guinea, at the north of the island. The Buka Passage separates the peninsula from Buka Island....
and contained; in the centre the seizure of Pearl Ridge
Battle of Pearl Ridge
The Battle of Pearl Ridge was a battle of the Second World War fought between Australian and Japanese forces on Bougainville Island. Part of the wider Bougainville Campaign, the battle took place in the central sector of the island, shortly after the Australians had taken over responsibility from...
would give the Australians control of the east–west avenues of approach, as well as affording them protection against further counter-attack
Counter-Attack
Counter-Attack is a 1945 war film starring Paul Muni and Marguerite Chapman as two Russians trapped in a collapsed building with seven enemy German soldiers during World War II...
s, while also opening the way for a drive to the east coast; and the main campaign in the south, where the bulk of the Japanese forces were concentrated. Allied estimates of Japanese strength were later found to be grossly inaccurate and after the war it was found that the number of Japanese alive on the island at this time was closer to 40,000.
Prelude
On 31 December Savige ordered Brigadier John Stevenson, commander of the 11th Brigade11th Brigade (Australia)
The Australian 11th Brigade is an Australian Army brigade which currently comprises most Australian Army Reserve units located in Queensland. The Brigade was first formed in early 1916 as part of the 3rd Division and saw action during World War I and World War II.-Brigade Structure:*Headquarters...
to begin clearing operations along the northeast coast of the island towards Soraken Harbour
Soraken
Soraken is a village on the Soraken Peninsula on northwestern Bouganville. The Soraken copra plantation was setup by Choisel Plantations in January 1913 and a tramway system long was constructed. The railway is now is disrepair...
, as they attempted to drive the Japanese in the sector on to the narrow Bonis Peninsula. At the time the Australians believed there to be around 390 Japanese defending the area surrounding the Genga River—considered to be the main Japanese defence line in the northern sector—however, it was later determined to be closer to 900 men from the 81st Infantry Regiment, under the command of Lieutenant Colonel Shinzo Nakamura. Nakamura, who was considered to be a "master of jungle warfare", had been ordered to prevent the Australian advance along the coast, but had perceived the likelihood of stopping them before the Genga as being unlikely and had as such decided that he would concentrate his defence around Tsimba Ridge, with supporting elements being placed to the north, near Kunamatoro.
Taking over control of the northern sector from the 7th Brigade, which was subsequently transferred to southern sector to take part in the main offensive, the 11th Brigade advanced along the coast from Kuraio Mission, sending out patrols into the interior to flush the Japanese out of their positions in the mountains as they went. The 31st/51st Battalion
31st/51st Battalion (Australia)
The 31st/51st Battalion was an infantry battalion of the Australian Army, which served during World War II. Raised for service as part of the Militia in 1943 through the amalgamation of two previously existing battalions, the 31st/51st Battalion undertook garrison duties in Dutch New Guinea in...
, under the command of Lieutenant Colonel Joseph Kelly formed the vanguard
Tactical formation
A tactical formation is the arrangement or deployment of moving military forces such as infantry, cavalry, AFVs, military aircraft, or naval vessels...
of the advance, its main body moving along the coast road towards Amun
Amun
Amun, reconstructed Egyptian Yamānu , was a god in Egyptian mythology who in the form of Amun-Ra became the focus of the most complex system of theology in Ancient Egypt...
, Sipaai and Rukussia, while patrols were sent inland from Totokei towards Lalum and Soraken
Soraken
Soraken is a village on the Soraken Peninsula on northwestern Bouganville. The Soraken copra plantation was setup by Choisel Plantations in January 1913 and a tramway system long was constructed. The railway is now is disrepair...
, both of which were considered key Japanese positions. By 16 January the lead company of the 31st/51st reached Rukussia, having encountered no Japanese up until that point.
Battle
The first contact came on 17 January when the 31st/51st Battalion's advanced elements—drawn mainly from 'D' Company—moved north from Rukussia and proceeded towards the Genga River. Reaching a clearing 1000 yards (914.4 m) north of Puto, a platoonPlatoon
A platoon is a military unit typically composed of two to four sections or squads and containing 16 to 50 soldiers. Platoons are organized into a company, which typically consists of three, four or five platoons. A platoon is typically the smallest military unit led by a commissioned officer—the...
-sized patrol came across a number of huts in a cleared area and proceeded to launch an attack on it. One Japanese was killed in the initial attack, however, as the Australians took the huts and pushed forward beyond them, they were engaged from entrenchments 100 yards (91.4 m) in front of them. The Japanese then proceeded to launch a counter-attack using light and heavy machine guns. In response, the Australians brought up another platoon and over the course of two days the counter-attack was repulsed, with six to eight Japanese estimated to have been killed and a number wounded, while two Australians were wounded.
During the engagement the Japanese had opened up with the artillery
Artillery
Originally applied to any group of infantry primarily armed with projectile weapons, artillery has over time become limited in meaning to refer only to those engines of war that operate by projection of munitions far beyond the range of effect of personal weapons...
that they had brought up in support of the main defensive position on Tsimba Ridge, firing for the first time in the sector; this barrage, however, proved largely ineffective, inflicting only one casualty, as many of the shells proved to be faulty and did not detonate. The Australians also came across large camp, including a field hospital, which they captured intact, while another group of huts was discovered, from where they gained intelligence identifying the Japanese troops in the area as belonging to the 81st Infantry Regiment. They also managed to capture two 70 mm guns, and a quantity of ammunition for them.
On 19 January the 31st/51st Battalion's 'A' Company sent a patrol out to outflank
Flanking maneuver
In military tactics, a flanking maneuver, also called a flank attack, is an attack on the sides of an opposing force. If a flanking maneuver succeeds, the opposing force would be surrounded from two or more directions, which significantly reduces the maneuverability of the outflanked force and its...
the Japanese forward positions; this patrol moved first to the right flank and then headed north along the tracks around Totokei and Goton. Discovering evidence of Japanese movement in the area, they followed these to the village of Kunamatoro, about 1 miles (1.6 km) north of Junapopo. Here they encountered a force of around 30 to 50 Japanese and after the initial contact, in which the Australian platoon commander was wounded, the patrol attacked the village. Within 10 minutes the battle was over: 14 Japanese had been killed, along with a further five wounded, while the Australians suffered one killed, one wounded and one missing. As darkness fell, the Australian patrol withdrew from the village.
The following day—20 January—the advanced elements of the Australian force pressed on towards Tsimba Ridge. A formation about 200 yards (182.9 m) long and about 60 feet (18.3 m) in height, and stretching westerly to the Genga River where a steep cliff
Cliff
In geography and geology, a cliff is a significant vertical, or near vertical, rock exposure. Cliffs are formed as erosion landforms due to the processes of erosion and weathering that produce them. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually...
fell to the southern bank of the river, the ridge blocked the Australian advance across the river, while its south-eastern most protrusion (later known as 'the Pimple') was separated by a shallow saddle. On top of the ridge, dense jungle provided good concealment
Concealment
Hiding is obscuring something from view or rendering it inconspicuous.Concealment is obscuring something from view or rendering it inconspicuous, the opposite of exposure...
, while the approaches to the ridge were largely open to observation. As the Australians approached the ridge, one of their platoons captured a 47 mm gun which had been positioned along the coast about 1000 yards (914.4 m) south of the ridge, while another platoon contacted a lone Japanese soldier, who was killed in the subsequent fire fight as they entered a garden that curved along the southern approach to the ridge, and which became known as 'the amphitheatre'. After the initial contact, the platoon's advance through the garden was prevented by an intense burst of fire from the ridge, however, the Australians proceeded to scale the high ground that rose to their east and subsequently they were able to occupy the south-eastern tip of the Pimple, capturing two 75 mm guns in the process.
Reports had been received from locals that the Japanese had brought reinforcements down from Soraken, Taiof Island and Tarlena and at this point the Australians realised that the Japanese had concentrated in far greater numbers than anticipated and had in fact established their line of resistance
Main Line of Resistance
Main Line of Resistance, or MLR is a military term describing the most important defensive position of an army facing an opposing force over an extended front...
in the sector upon the ridge. This was confirmed later after the Australians moved forward once more on 21 January, moving to within 800 yards (731.5 m) from the Genga River, where the track upon which they were advancing opened into a large garden, which curved around the edge of Tsimba Ridge, from where the Japanese defenders had an excellent line of sight. Subsequent patrols determined the extent of the Japanese position, reporting that they had constructed a well fortified position with a continuous trench along the crest of ridge, weapons pits and pill boxes, all with clear fields of fire, stretching up to 150 yards (137.2 m).
The Australian commander, Kelly, ordered 'B' Company to move up and take the ridge and over the course of a week between 21–28 January they made a number of attempts. These proved fruitless, however, although one platoon managed to encircle the position from the north before being engaged with heavy machine gun
Machine gun
A machine gun is a fully automatic mounted or portable firearm, usually designed to fire rounds in quick succession from an ammunition belt or large-capacity magazine, typically at a rate of several hundred rounds per minute....
fire. On 23 January, the Australians established fire support in the form of guns from the 2nd Mountain Battery
A Field Battery, Royal Australian Artillery
A' Field Battery is an airborne artillery battery of the Australian Army. The unit has been in existence since 1871, having originally been raised as part of the New South Wales colonial defence force...
. Another three unsuccessful attempts were made on 24 January, while on 25 January 'C' Company carried out a movement to the flank in an attempt to get around behind the ridge and attack from the north. Crossing the crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...
-infested waters of the Genga about 600 yards (548.6 m) from the ridge, the Australians established a bridgehead
Bridgehead
A bridgehead is a High Middle Ages military term, which antedating the invention of cannons was in the original meaning expressly a referent term to the military fortification that protects the end of a bridge...
across the river with a line of communication
Line of communication
A line of communication is the route that connects an operating military unit with its supply base. Supplies and reinforcements are transported along the line of communication. Therefore, a secure and open line of communication is vital for any military force to continue to operate effectively...
s back to the Pimple, which they kept open by maintaining a constant patrol along it.
Over the following six days, the Japanese proceeded to attack the bridgehead, launching a number of attacks that bordered upon suicidal. These attacks were repulsed, however, and the Australians began to launch patrols in all directions around the ridge. On 29 January the Japanese launched a large scale attack on 'C' Company's positions and although the Australians resisted stubbornly, the attack succeeded in breaking through one part of the perimeter and managed to roll up the position all the way to the main battalion position around Puto before it was turned back. The Australian counter-attack, organised by the 'C' Company's commander, Captain Alwyn Shilton, and supported by accurate artillery fire, came on 1 February and resulted in over 30 Japanese killed or wounded.
For the next few days further probes were made by the Japanese, however, these were also repulsed and the Australians consolidated their positions in preparation for an assault on the ridge. Preparations at this time included the manhandling of a mountain gun from Puto to a position 150 yards (137.2 m) from the Pimple, from where it could fire directly upon the Japanese positions on the ridge, while aircraft from No. 5 Squadron, Royal Australian Air Force
No. 5 Squadron RAAF
No. 5 Squadron was a Royal Australian Air Force training, army co-operation and helicopter squadron. The Squadron was first formed in 1917 and was disbanded in December 1989.-Squadron history:...
carried out reconnaisance. In order to maintain the secrecy of these preparations, mortar
Mortar (weapon)
A mortar is an indirect fire weapon that fires explosive projectiles known as bombs at low velocities, short ranges, and high-arcing ballistic trajectories. It is typically muzzle-loading and has a barrel length less than 15 times its caliber....
fire was brought down upon the Japanese positions to mask the sounds of digging and movement while machine gun fire from Vickers machine gun
Vickers machine gun
Not to be confused with the Vickers light machine gunThe Vickers machine gun or Vickers gun is a name primarily used to refer to the water-cooled .303 inch machine gun produced by Vickers Limited, originally for the British Army...
s kept the Japanese defenders from being able to leave their shelter and observe.
The attack finally came on 6 February. Supported by a barrage of over 500 artillery shells and mortar bombs, three platoons from 'B' Company assaulted the ridge from different points in an effort to encircle the defenders. Following the artillery preparation fire, the attack began at 0900 hours when two platoons—10 and 11 Platoons—along with company headquarters formed up south-east of the amphitheatre and began to advance to the north-west 200 yards (182.9 m) to attack the ridge from behind, while another force—12 Platoon—attacked from the garden, moving around the Pimple before assaulting the ridge from east.
From the north-west, 10 Platoon, in the centre, managed to capture its objectives by 0925 hours, however, 12 Platoon, came under intense fire and after suffering several casualties stopped their advance. By 1130 hours the most northern Australian platoon, 11 Platoon, had reached the high ground on the north-western side of the ridge, completing the encirclement of the Japanese, however, the defenders refused to give up the position. The attack cost the Australians nine killed and 20 wounded. The next day the Japanese launched a counter-attack which, although repulsed, enabled them to continue to maintain a small pocket of resistance on the western tip of the ridge; this was finally abandoned on 9 February, however, when an airstrike
Airstrike
An air strike is an attack on a specific objective by military aircraft during an offensive mission. Air strikes are commonly delivered from aircraft such as fighters, bombers, ground attack aircraft, attack helicopters, and others...
was called in upon the position and the Japanese withdrew from the feature.
Aftermath
It was estimated that 66 Japanese had been killed defending the ridge. The Australians also captured a large amount of equipment, including four field and six anti-tank guns, nine machine guns and 86 rifles. Australian casualties were approximately 23 killed and 53 wounded. From documents captured after the war, the Japanese believed that these losses would slow the Australian advance down. At the time they did not perceive the loss of Tsimba Ridge to be a defeat. They had been prepared to hold the position, and had the numbers to do it, however, Nakamura had decided to withdraw from the ridge when the morale of his troops had fallen due to lack of ammunition and food and rising casualties from tropical diseases.After the fall of Tsimba Ridge, fighting continued around the Genga River for the next couple of weeks. On 10 February area south the Genga had been cleared of Japanese and the Australians began to patrol along the northern bank. A number of minor clashes occurred, the most serious of which saw three Japanese killed and three Australians wounded in an action in which the Australians managed to capture a Japanese 37 mm gun. As the Japanese were forced to withdraw from a position along the track which ran 150 yards (137.2 m) from the river, the Japanese artillery intensified and a number of men from the 31st/51st Battalion became casualties.
The 31st/51st Battalion continued operations around the Genga River until 22 February, when they were relieved by the 26th Battalion, who continued the advance north towards Ratsua
Battle of Ratsua
The Battle of Ratsua occurred during the Second World War and involved Australian and Japanese forces. Part of the wider Bougainville Campaign of the Pacific theatre, the battle took place in the northern sector of Bougainville between June and August 1945...
. In total, the Australians lost 34 killed and 91 wounded in the fighting around the Genga River, while it was estimated that the Japanese lost 148 killed.
For their involvement in taking Tsimba Ridge, the 31st/51st Battalion were awarded the battle honour
Battle honour
A battle honour is an award of a right by a government or sovereign to a military unit to emblazon the name of a battle or operation on its flags , uniforms or other accessories where ornamentation is possible....
"Tsimba Ridge".