"The direct attack on the German positions in and around San Pietro began on 8 December by Major General Geoffrey Keyes' II Corps of the Fifth Army. The positions were defended by two battalion sized elements of the 15th Panzer Grenadier Division and a battalion of the 71st Infanterie Division, all part of German Tenth Army's XIV Panzer Corps.
After a week of intense attacks and counterattacks, the U.S. 36th Division's 143rd Infantry Regiment the 3rd Ranger Battalion and the 504th Parachute Regimental Combat Team (504th PRCT) commanded the heights of the Sambúcaro mass. The U.S. 36th Division, then planned a further effort for 15 December.
The 143rd Infantry, assisted by the 504th PRCT, would continue to push west along the shoulders of Sambúcaro and take San Vittore del Lazio while to the south of Route 6 the 142nd Infantry, supported by the Italian 1st Motorized Group, were to capture Mount Lungo. In the center, the 141st Infantry would attack San Pietro itself. The main attack of the 36th Division started at 12:00 on 15 December. In an effort to break the German defenses in the town, two platoons from the 753rd Tank Battalion attacked with 16 Sherman tank and tank destroyers.
The armored attack failed due to mines and anti-tank fire. Four of the 16 tanks survived. After four successive Allied attacks and German counterattacks, the Germans pulled back from San Pietro since the dominating ground on both flanks, Mount Lungo and the Sambúcaro peaks, was now in II Corps' possession. The Germans launched a counterattack on 16 December to cover their withdrawal as they retreated to positions farther north at Cedro Hill, Mount Porchia, San Vittore, and the western spurs of Sambcaro. "