 By 8 April, after meeting stiff resistance, it had completed its task in clearing "the Wedge", an area from the southern tip of Lake Comacchio where it meets the Reno river to the Fossa di Navigazione.The main Eighth Army offensive across the Senio river commenced on 9 April and by 12 April the assault units had advanced to consolidate across the Santerno river and allow 78th Infantry Division to pass through towards the Reno river and the Argenta gap.The Argenta Gap was a well defended strip of land some wide and deep between Lake Comacchio and the Lombardy marshes, south of the town of Ferrara.