In early November 1943, the 3rd Marine Division, under Major General Allen H. Turnage, landed at Cape Torokina near Empress Augusta Bay on the western coast of Bougainville.
The landing took place as part of Allied efforts to advance towards the main Japanese base around Rabaul, the isolation and reduction of which was a key objective of Operation Cartwheel.
Opposing the US troops at Cape Torokina were troops of Lieutenant General Harukichi Hyakutake's   Japanese 17th Army, part of  General Hitoshi Imamura's 8th Area Army, based at Rabaul.
The bulk of the infantry forces were drawn from the 6th Division, under Lieutenant General Masatane Kanda.

Following the landing, a series of battles were fought around the beachhead, which was slowly expanded by the Marines out to about 8–10 kilometers (5.0–6.2 mi) by the end of the month.
Throughout November, the Japanese had begun moving artillery pieces into position around the perimeter and began shelling the beachhead from several hills to the east of the Numa–Numa and East–West Trails, along the Torokina River.
Following the fighting around Piva Forks in late November, plans were drawn up by US commanders to advance towards the Torokina River where a series of high features offered significant defensive advantages that could be exploited in the event of a Japanese counterattack, which US intelligence expected.
The general outline of the US plan was to establish a defensive line parallel to the Torokina, along a ridge line that extended to the west from a position in the north known as Hill 1000 to Hill 600A in the south.

On 5 December, the US advance began and several minor clashes between patrol-sized elements took place.
Two days later, Marines from the 3rd Parachute Battalion met resistance along a spur to the west of Eagle Creek, at a position north of the junction of the East–West Trail near Hill 1000, which later became known to US troops as "Hellzapoppin Ridge" due to its difficult terrain, part of a feature the Japanese dubbed "Picha Mountain".
Documents captured by the advancing Marines indicated that a reinforced company of 235 men from the Japanese 23rd Infantry Regiment was holding the position.
The hill, due to its position, threatened the flank of the 3rd Parachute Battalion's position and as a result, the Marine commander was forced to readjust his dispositions to place the spur to his front.
After consolidating their position and sending out patrols, a number of minor skirmishes took place before the Paramarines launched a company-level attack on the morning of 9 December.
Although they managed to break-in to the Japanese position, the Marines were forced back by determined Japanese resistance, having sustained heavy casualties.
A flanking maneuver also failed to dislodge the defenders.
Late in the day, a company from the 1st Battalion, 21st Marines was sent up to reinforce the Paramarines and the following day the rest of the 21st Marine Regiment, under the command of Colonel Evans O. Ames, arrived to take over responsibility for capturing the spur line around Hill 1000.
In early November 1943, the 3rd Marine Division, under Major General Allen H. Turnage, landed at Cape Torokina near Empress Augusta Bay on the western coast of Bougainville. The landing took place as part of Allied efforts to advance towards the main Japanese base around Rabaul, the isolation and reduction of which was a key objective of Operation Cartwheel. Opposing the US troops at Cape Torokina were troops of Lieutenant General Harukichi Hyakutake's   Japanese 17th Army, part of  General Hitoshi Imamura's 8th Area Army, based at Rabaul.The bulk of the infantry forces were drawn from the 6th Division, under Lieutenant General Masatane Kanda. 
Following the landing, a series of battles were fought around the beachhead, which was slowly expanded by the Marines out to about 8–10 kilometers (5.0–6.2 mi) by the end of the month. Throughout November, the Japanese had begun moving artillery pieces into position around the perimeter and began shelling the beachhead from several hills to the east of the Numa–Numa and East–West Trails, along the Torokina River. Following the fighting around Piva Forks in late November, plans were drawn up by US commanders to advance towards the Torokina River where a series of high features offered significant defensive advantages that could be exploited in the event of a Japanese counterattack, which US intelligence expected. The general outline of the US plan was to establish a defensive line parallel to the Torokina, along a ridge line that extended to the west from a position in the north known as Hill 1000 to Hill 600A in the south.
On 5 December, the US advance began and several minor clashes between patrol-sized elements took place. Two days later, Marines from the 3rd Parachute Battalion met resistance along a spur to the west of Eagle Creek, at a position north of the junction of the East–West Trail near Hill 1000, which later became known to US troops as "Hellzapoppin Ridge" due to its difficult terrain, part of a feature the Japanese dubbed "Picha Mountain". Documents captured by the advancing Marines indicated that a reinforced company of 235 men from the Japanese 23rd Infantry Regiment was holding the position. The hill, due to its position, threatened the flank of the 3rd Parachute Battalion's position and as a result, the Marine commander was forced to readjust his dispositions to place the spur to his front. After consolidating their position and sending out patrols, a number of minor skirmishes took place before the Paramarines launched a company-level attack on the morning of 9 December. Although they managed to break-in to the Japanese position, the Marines were forced back by determined Japanese resistance, having sustained heavy casualties. A flanking maneuver also failed to dislodge the defenders. Late in the day, a company from the 1st Battalion, 21st Marines was sent up to reinforce the Paramarines and the following day the rest of the 21st Marine Regiment, under the command of Colonel Evans O. Ames, arrived to take over responsibility for capturing the spur line around Hill 1000.
Battle of Hellzapoppin Ridge and Hill 600A