"During the last week in August, U.S. II Corps and British XIII Corps started to move into the mountains to take up positions for the main assault on the main Gothic Line defences. Some fierce resistance was met from outposts but at the end of the first week in September, once reorganisation had taken place following the withdrawal of three divisions to reinforce the pressured Adriatic front, the Germans withdrew to the main Gothic Line defences. After an artillery bombardment, the Fifth Army's main assault began at dusk on 12 September. Keyes tried to flank the II Giogo Pass by attacking both the peaks of Monticello and Monte Altuzzo using the 91st Infantry Division (nicknamed the "Wild West Division") in a bold attempt to bounce the Germans off the positions, but this failed.
Progress at the II Giogo Pass was slow, but on II Corps' right British XIII Corps were making better progress. Clark grasped this opportunity to divert part of II Corps reserve (the 337th Infantry Regiment, part of the 85th Infantry Division) to exploit XIII Corps success. Attacking on 17 September, supported by both American and British artillery, the infantry fought their way onto Monte Pratone, some 2–3 mi (3.2–4.8 km) east of the Il Giogo pass and a key position on the Gothic Line. Meanwhile, U.S. II Corps renewed their assault on Monte Altuzzo, dominating the east side of the Il Giogo Pass. The Altuzzo positions fell on the morning of 17 September, after five days of fighting. The capture of Altuzzo and Pratone as well as Monte Verruca between them caused the formidable Futa Pass defences to be outflanked, and Lemelsen was forced to pull back, leaving the pass to be taken after only light fighting on 22 September."