The USAFP was composed of five infantry regiments and a field artillery battalion of about 20,000 men, all Filipinos except for five American officers, and commanded by Col. Russell W. Volckmann. The troops bore the brunt of the fighting, sustaining over 3,375 casualties, including over 900 men killed, from 9 Jan. through 15 June 1945. The units of the USAFP that fought at the battle were the 121st, 15th, 66th, the Provisional Battalion, and the 122nd Field Artillery. They faced the 73rd Infantry and the 76th Infantry, part of the 19th Division led by Lt. General Yoshiharu Ozaki. The Japanese forces fortified the hills and the ridges to stop any American offensive on the way to Cervantes and the Cordillera stronghold of Yamashita. The initial fighting started in February 1945 with an advance inland to the town of Cervantes by the 121st Infantry. After liberating San Fernando, La Union, on 23 March, the USAFP-NL forces started the all-out assault on Bessang Pass. However, on 17 May, the 73rd Infantry, 19th Division, made a strong counterattack, pushing back the 121st. On 1 June, Volckmann started his renewed attack with three regiments abreast. They cleared the Lamagan and Lower Cadsu Ridges by 5 June. Magun Hill was captured by 10 June, and the Upper Cadsu Ridge was taken by 12 June. On 10 June, the units of 121st launched a final assault and by 14 June, the "last opposition melted away". Cervantes was secured by 15 June.
Aftermath
The USAFP, according to Smith, "made a substantial contribution toward the Sixth Army's campaign in northern Luzon...the USAFIP had kept the 19th Division pinned to the triangle formed by Bontoc, KP 90, and Bessang Pass...seizing San Fernando and clearing Route 3 up the west coast, the USAFIP had permitted the Sixth Army to forget about plans to use a 'regular' division along the coast." Additionally, Smith said, "the USAFIP accomplished far more than GHQ SWPA, Sixth Army, or I Corps had apparently expected or hoped." According to Robert Lapham, "so generally hated was...Capt. Emilio Escobar and his guerrilla band...most of his men were killed by other guerrillas rather than by the Japanese", due to their having "committed numberless horrifying personal crimes,...thought to have murdered some three thousand to four thousand civilians."