The Battle of Piva Forks, also known as the Battle of Numa–Numa Trail, was an engagement that took place during the Bougainville campaign in World War II. Occurring between 18 and 25 November 1943 on Bougainville Island in the South Pacific, the battle involved troops from the United States Marine Corps and the United States Army fighting against Imperial Japanese Army forces and took place amidst the context of the expansion of a beachhead that US forces had established around Torokina on the western side of the island.
In response to the US forward movement, the Japanese placed road blocks along the main axes of advance to delay the Americans; finding their way towards the Piva River checked near the junction of the Numa–Numa and East–West Trails, the US forces sought to remove the obstacles by force. After the initial US attack was repulsed, the Japanese counterattacked before the US Marines overcame this and continued their advance towards two forks in the Piva River. By 26 November the battle had subsided following the capture of a knoll overlooking the East–West Trail by US forces. This represented the last of the significant features west of the Torokina, and the conclusion of the battle marked a temporary end to significant Japanese opposition to the US beachhead around Torokina.
Background
On 1 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 landings were undertaken as part of Allied efforts to isolate and reduce the main Japanese base around Rabaul under Operation Cartwheel. On Bougainville, the Marines were opposed by Lieutenant General Harukichi Hyakutake's Japanese 17th Army, which formed part of General Hitoshi Imamura's 8th Area Army, based at Rabaul. The main infantry forces opposing the Marines were the 6th Division, under Lieutenant General Masatane Kanda.
Following the landing, a counter landing by Japanese troops was turned back around Koromokina Lagoon, while an overland assault was turned back along the Piva Trail. After this, the beachhead was slowly expanded by the Marines while work began to construct several airfields, from which airpower would be projected towards Rabaul. After the Battle of the Coconut Grove on 13–14 November, American patrols reported sporadic contacts with Japanese forces. Documents obtained from a Japanese officer who was killed in an ambush provided US forces with details of Japanese dispositions in the area, showing that a roadblock had been set up by elements of the Japanese 23rd Infantry Regiment on both the Numa–Numa and the East–West Trails. General Roy Geiger, commander of I Marine Amphibious Corps, set in place plans for the expansion of the beachhead perimeter that had been established around Torokina to a new defensive line further inland designated as "Easy". Geiger specified that the line was to be obtained by 20 November 1943. On 18 November, US patrols discovered a Japanese roadblock on the Numa–Numa Trail about 1,000 yd (910 m) in front of the beachhead perimeter lines, while another patrol found a roadblock halfway between the two branches of the Piva River along the East–West Trail.
With the roadblocks serving as obstacles to their advance to the Inland Defense Line "Easy", preparations were undertaken by US forces to remove these roadblocks. The 3rd Marine Raider Battalion was attached to Colonel George W. McHenry's 3rd Marine Regiment for the attack on the East–West Trail roadblock, while the 3rd Battalion, 3rd Marines—under the command of Lieutenant Colonel Ralph M. King—was detached to attack the Numa–Numa Trail roadblock.
Battle
On 19 November, the 3rd Battalion, 3rd Marine Regiment—accompanied by light tanks—took up positions in front of the 129th Infantry Regiment. An artillery barrage by the 12th Marine Regiment preceded the attack; after it had ceased the 3rd Battalion, 3rd Marine Regiment flanked the Japanese position, routing the defenders and forcing them out of their positions. Sixteen Japanese dead were found and almost 100 foxholes located; the size of the position indicated that at least a reinforced company had occupied it. After this, a roadblock and a defensive perimeter were established at the junction of the Numa–Numa Trail and the Piva River to defend against a potential Japanese counterattack. Meanwhile, the 1st Battalion, 3rd Marine Regiment and the 1st Battalion, 21st Marine Regiment advanced to the 3rd Battalion, 3rd Marine Regiment roadblock. The 3rd Marine Raiders also moved forward for support and the 2nd Battalion, 3rd Marine Regiment—under the command of Lieutenant Colonel Hector de Zayas—moved behind the Numa–Numa Trail roadblock and was sporadically shelled by the Japanese using 90 mm mortars.
On the morning of 20 November, the Japanese counterattacked and attempted to outflank the Marine positions along the Numa–Numa Trail. The attack was driven back, taking up positions and then harassed the Marines with sniper fire and mortar fire. The 3rd Battalion, 3rd Marine Regiment advanced towards the two forks of the Piva River to clear the threat, and two light tanks were disabled during the close fighting along the trail. The 3rd Marine Raiders took up positions to cover the gap between the 129th Infantry Regiment and the 3rd Marine Regiment as the front expanded.
The 2nd Battalion, 3rd Marine Regiment advanced across the west fork of the Piva River to capture the Japanese positions between the two forks of the river. A river crossing was made using a hastily constructed bridge of mahogany, constructed by engineers. Moving forward under light opposition from scattered snipers and several machine gun nests, the enemy outposts were discovered to have been abandoned and had been booby-trapped. The 2nd Battalion, 3rd Marine Regiment set up positions astride the East–West Trail between the two forks of the river. The 21st Marine Regiment took up blocking positions behind the 3rd Marine Regiment.
Late in the afternoon of 20 November, a small, 400 ft (120 m) high ridge was discovered that would provide observation of the entire Empress Augusta Bay area and dominated the East–West Trail and the Piva Forks area. A platoon—under the command of First Lieutenant Steve J. Cibik—was ordered to occupy the ridge with detachments of signals and a section of heavy machine guns. The trek began with a struggle up the steep ridge late in the afternoon, with signal wire being reeled out as the platoon climbed the ridge. Reaching the summit just before sunset, they set about establishing defensive positions, with machine guns sited along likely avenues of attack.
With daybreak on 21 November, it was discovered that the crest of the ridge was a Japanese outpost position, used during the day as an observation post and abandoned at night. Approaching Japanese soldiers who were preparing to take up positions were fired upon, and they withdrew and fled down the hill. The enemy, having regrouped and having been reinforced, launched numerous attacks against Cibik's platoon, which had been reinforced by more machine guns and mortars and was able to hold onto the crest despite fanatical attempts by the Japanese to reoccupy the position.
Geiger's expansion of the beachhead to Inland Defense Line "Easy" began at 07:30 on 21 November, with the gradual widening of the perimeter allowing the 21st Marine Regiment, under the command of Colonel Evans O. Ames, to set up positions between the 3rd Marine Regiment and the 9th Marine Regiment. The 1st Battalion and 3rd Battalion of the 21st Marine Regiment led the way, crossed the Piva River without difficulty and by early afternoon had reached the designated defense line. On the extreme left flank, a reinforced platoon was attacked by a strong Japanese patrol. The platoon was able to repulse the attack with heavy losses to the enemy; documents discovered on a dead Japanese officer provided the Marines with details about the state of Japanese defenses ahead of them.
Resistance to the 3rd Marine Regiment advance was strong, with all three battalions engaged with the Japanese. The 3rd Battalion, 3rd Marine Regiment—having crossed the Piva River without trouble—advanced toward a slight rise, and as the lead scouts came over the top of this ridge, the Japanese opened fire from reverse slope positions. Pinned down, the scouts held their positions while the rest of the battalion moved forward with a strong charge over the ridge and cleared the area of Japanese. 90 mm mortar fire then rained down on the Marines, who sheltered in the foxholes that the Japanese had dug throughout the area. Suffering a number of casualties, the 3rd Battalion, 3rd Marine Regiment established itself in a defensive night position.
The 2nd Battalion, 3rd Marine Regiment made a reconnaissance in force in front of the 1st Battalion, 3rd Marine Regiment positions and came along a strong enemy position, with about 18–20 pillboxes, astride the East–West Trail near the east fork of the river. An attack was launched against the roadblock and managed to pass through the first line of bunkers after heavy fighting at close range but could make no further headway. Company E—attempting to flank the enemy positions to relieve the intense fire directed at Company G—was knocked back by the Japanese defenders. As the Japanese position was set out in depth, de Zayas ordered his men to pull back so that an artillery barrage could be brought down to reduce the Japanese defenses.
The withdrawal was completed despite determined efforts by the Japanese to prevent the disengagement. After the 2nd Battalion, 3rd Marine Regiment had reentered the lines of 1st Battalion, 3rd Marine Regiment, the Japanese attempted a pincer envelopment of the position held by the 1st Battalion, 3rd Marine Regiment, now under the command of Major Charles J. Bailey Jr. The Japanese attacked along the obvious routes of approach down the East–West Trail, and the attack was beaten off by the machine guns sited along this route. One machine gun crew killed 74 out of 75 of the Japanese attackers within 20–30 yards (18–27 m) of the gun. The 1st Battalion, 3rd Marine Regiment then extended to the left toward the ridge occupied by Cibik's platoon.
The 9th Marine Regiment crossed the Piva River took up defensive positions about 1,000 yd (910 m) east of the river, between the 21st Marine Regiment and the beach. The 129th Infantry Regiment also moved forward another 1,000 yd (910 m) unopposed. As a result of inaccurate maps, a gap developed between the 21st Marine Regiment and the 3rd Marine Regiment. At this point, US forces paused in their perimeter expansion of the perimeter as Japanese forces were well dug-in to their front. Plans were drawn up to attack the enemy fortifications, and preparations for the 24 November assault were undertaken. As armor and equipment was moved into positions behind the 3rd Marine Regiment, the roads were extended by engineers and Seabees who advanced them as close to the river forks as possible. Operating under fire from Japanese snipers and mortars, they erected bridges across the river, and large quantities of supplies of ammunition, rations, and medical supplies were sent forward via a relay system to the front lines, while wounded were tended to at a medical station that had been set up close to the end of the road prior to evacuation.
The 2nd Marine Raider Battalion was attached to the 3rd Marine Regiment during 22 November and relieved the 3rd Battalion, 3rd Marine Regiment, which moved into reserve. The 3rd Marine Regiment's positions were: 1st Battalion, 3rd Marine Regiment in front, with 3rd Battalion, 3rd Marine Regiment on the left of the trail and the 2nd Battalion, 3rd Marine Regiment on the right. Cibik's reinforced platoon holding the ridge in front of the perimeter, was reinforced with a company of Marine Raiders and a platoon from the 3rd Marines Weapons Company.
On 23 November, the 12th Marine Regiment's artillery observers moved to the crest of the ridge occupied by Cibik's platoon, in preparation for the attack the next day. As the US artillery and mortars were registered in the area in front of their position, the Marines on the front lines used colored smoke grenades to mark their positions. The Japanese, however, were using the same colors to mark US positions and, as a result the Japanese artillery were able to range in on the forward Marine positions with several rounds. Japanese long-range guns also shelled Torokina Airfield and Landing Ship Tanks that were unloading near Cape Torokina. In response, US forward artillery observers coordinated fire missions against several positions where they believed that the Japanese guns might be located, and shortly after this the firing ceased. Nevertheless, the Japanese artillery fire worried US commanders who were already concerned about reports that the size of Japanese forces defending the area around the village of Kogubikopai-ai was between 1,200 and 1,500.