The US advance from Zanana to Munda was completely stymied, hampered by difficult terrain, supply problems and low morale. General Hester tried to break the stalemate by sending the 172nd Infantry Regiment around to the north to take the Japanese position in the rear, while the 169th Infantry Regiment continued the frontal assault, but this effort was checked by Sasaki. As a result, the US advance on New Georgia stalled in both the north and the south. The Japanese brought reinforcements by barge from Vila to Bairoko, and 1,200 more troops were loaded onto four destroyer-transports at Rabaul and sent down to be landed at Vila on the night of 12–13 July. These ships were escorted by a light cruiser and five destroyers. Admiral Ainsworth was sent to intercept this flotilla with three light cruisers and ten destroyers. He encountered the Japanese force in The Slot in the waters north of Kolombangara Island and in the ensuing Battle of Kolombangara one US destroyer and one Japanese light cruiser were sunk.