On the evening of 11/12 July, a naval task force under Rear Admiral Aaron S. Merrill, having departed Ironbottom Sound in the afternoon, fired over 8,600 shells during a 40-minute bombardment from the Blanche Channel to clear the jungle in front of the advancing troops; this ultimately proved ineffective, being fired over a mile in front of the U.S. troops for safety reasons. The following day, the 172nd resumed their advance but made only limited progress. Allied efforts to interdict the Munda trail from the north proved unsuccessful, and during this time the Japanese were able to land reinforcements from 16 barges that sailed from Vila; Japanese operations to move further reinforcements through the Slot on 12/13 July led to the naval Battle of Kolombangara. On 12 July, three battalions from the U.S. 169th Infantry Regiment carried out an attack against Japanese positions overlooking the junction of the Munda–Lambeti trail. The 1st and 2nd Battalions carried the attack initially, but were held up. The following day, the 3rd Battalion, 169th Infantry Regiment gained the south ridge—later dubbed "Reincke Ridge"—after several hours of fighting supported by dive bombers and artillery. A Japanese battalion found a gap in the line between the 169th and 172nd Infantry Regiments on 13 July, having resulted from the 172nd's diversion to Laiana, cutting off the American regiment around the high ground. They were then subjected to repeated counterattacks over the course of several days, resulting in over one hundred casualties on the first day alone. The 172nd finally reached their objective at Laiana on 13 July, having found the going difficult to push through the swamp and coming under Japanese mortar fire. By the time they reached the beach, the regiment was running short of water and supplies. The following day, a second landing was carried out at Laiana, in an effort to shorten lines of supply and bring in reinforcements from the 3rd Battalion, 103rd Infantry Regiment, which linked up with the 172nd. As part of efforts to break through to the cut-off 169th, the U.S. Army 118th Engineers, having previously pushed a track from Zanana, bridged the Barike River and ran a jeep trail towards the 169th's lines. Japanese troops harassed the bulldozer operators throughout this effort. Stores were moved to the head of this trail by an antitank company, but by 14 July it was still short. To relieve the supply situation, the 169th received supplies by parachute on 14 July.