After aerial bombardment and preparatory artillery fire, Buse's battalion started up the hill at about 0930 on 13 January. His supporting tanks could not negotiate the ravines that scarred the hillside. Indeed, the going became so steep that riflemen sometimes had to sling arms, seize handholds among the vines, and pull themselves upward. The Japanese suddenly opened fire from hurriedly dug trenches at the crest, pinning down the Marines climbing toward them until mortar fire silenced the enemy weapons, which lacked overhead cover. Buse's riflemen followed closely behind the mortar barrage, scattering the defenders, some of whom tried to escape along the coastal trail, where Buckley's task force waited to cut them down.
Apparently delayed by torrential rain, the Japanese did not counterattack Hill 660 until 16 January. Roughly two companies of Katayama's troops stormed up the southwestern slope only to be slaughtered by mortar, artillery, and small-arms fire. Many of those lucky enough to survive tried to break through Buckley's roadblock, where 48 of the enemy perished.
With the capture of Hill 660, the nature of the campaign changed. The assault phase had captured its objective and eliminated the possibility of a Japanese counterattack against the airfield complex. Next, the Marines would repulse the Japanese who harassed the secondary beachhead at Cape Merkus and secure the mountainous, jungle-covered interior of Cape Gloucester, south of the airfields and between the Green and Yellow Beaches.
The Mopping-up Begins in the West
At Cape Merkus on the south coast of western New Britain, the fighting proved desultory in comparison to the violent struggle in the vicinity of Cape Gloucester. The Japanese in the south remained content to take advantage of the dense jungle and contain the 112th Cavalry on the Cape Merkus peninsula. Major Shinjiro Komori, the Japanese commander there, believed that the landing force intended to capture an abandoned airfield at Cape Merkus, an installation that did not figure in American plans. A series of concealed bunkers, boasting integrated fields of fire, held the lightly armed cavalrymen in check, as the defenders directed harassing fire at the beachhead.
Because the cavalry unit lacked heavy weapons, a call went out for those of the 1st Marine Division's tanks that had remained behind at Finschhafen, New Guinea, because armor enough was already churning up the mud of Cape Gloucester. Company B, 1st Marine Tank Battalion, with 18 M5A1 light tanks mounting 37mm guns, and the 2d Battalion, 158th Infantry, arrived at Cape Merkus, moved into position by 15 January and attacked on the following day. A squadron of Army Air Forces B-24s dropped 1,000-pound bombs on the jungle-covered defenses, B-25s followed up, and mortars and artillery joined in the bombardment, after which two platoons of tanks, ten vehicles in all, and two companies of infantry surged forward. Some of the tanks bogged down in the rain-soaked soil, and tank retrievers had to pull them free. Despite mud and nearly impenetrable thickets, the tank-infantry teams found and destroyed most of the bunkers. Having eliminated the source of harassing fire, the troops pulled back after destroying a tank immobilized by a thrown track so that the enemy could not use it as a pillbox. Another tank, trapped in a crater, also was earmarked for destruction, but Army engineers managed to free it and bring it back.
The attack on 16 January broke the back of Japanese resistance. Komori ordered a retreat to the vicinity of the airstrip, but the 112th Cavalry launched an attack that caught the slowly moving defenders and inflicted further casualties. By the time the enemy dug in to defend the airfield, which the Americans had no intention of seizing, Komori's men had suffered 116 killed, 117 wounded, 14 dead of disease, and another 80 too ill to fight. The Japanese hung on despite sickness and starvation, until 24 February, when Komori received orders to join in a general retreat by Matsuda Force.
Across the island, after the victories at Walt's Ridge and Hill 660, the 5th Marines concentrated on seizing control of the shores of Borgen Bay, immediately to the east. Major Barba's 1st Battalion followed the coastal trail until 20 January, when the column collided with a Japanese stronghold at Natamo Point. Translations of documents captured earlier in the fighting revealed that at least one platoon, supported by automatic weapons had dug in there. Artillery and air strikes failed to suppress the Japanese fire, demonstrating that the captured papers were sadly out of date, since at least a company—armed with 20mm, 37mm, and 75mm weapons—checked the advance. Marine reinforcements, including medium tanks, arrived in landing craft on 23 January, and that afternoon, supported by artillery and a rocket-firing DUKW, Companies C and D overran Natamo Point. The battalion commander then dispatched patrols inland along the west bank of the Natamo River to outflank the strong positions on the east bank near the mouth of the stream. While the Marines were executing this maneuver, the Japanese abandoned their prepared defenses and retreated eastward.
