On 28 November the 40th Infantry Division was concentrated at Borgen Bay to prepare for the invasion of Luzon, the largest and most strategically important of the Philippine Islands. The 108th Regimental Combat Team—composed of the 108th Infantry Regiment, the 164th Field Artillery Battalion, Co. C of the 115th Engineer Combat Battalion, and Co. C of the 115th Medical Battalion—was in reserve on S-Day—9 January 1945, when the Sixth Army landed at Lingayen Gulf. Japanese resistance intensified as the GIs moved south toward Manila, and the 108th fought brutal battles for possession of Fort Stotsenburg, Clark Field, Top of the World, Hill 7, and Sacobia Ridge. The 43rd Infantry Division relieved the 40th on 2 March. Six days later the 108th was detached and sent to the island of Leyte to assist in mopping up defeated Japanese forces. The regiment's 2nd Battalion also cleared Masbate and other local islands. On Leyte and Masbate the 108th lost an estimated 19 troops killed and 49 wounded.