On 9 January, Japanese forces under Lt. Gen. Susumu Morioka attacked the eastern side of the Abucay-Mauban line. They were beaten by the U.S. The Japanese advanced to the Salian River valley. U.S. troops fought off the attackers. At another battle to the west, a Japanese force got past the Abucay-Mauban line. The U.S. stopped their advance. On 15 January, 1st Regular Division was bombed, but they held the line. The Japanese moved through a gap. The Abucay-Mauban line had to be abandoned on 22 January.