Overview of the Operation.
On the night of 10/11 April, British V Corps launched Operation Impact Plain to widen and deepen its bridgehead in the Wedge: 40th (Royal Marine) Commando advanced along the raised causeway bordering the lake while, from 56th (London) Division, 169th (Queen's) Brigade advanced on the commando's left across the flooded margins of the lake with two battalions in LVTs. The 56th Division's 167th Brigade advanced from the Wedge along the Reno flood banks. The commando column met stiff resistance at the bridge north east of Menate and took heavy casualties but were able to take the objective with the assistance of air support. 42nd Jaeger Division seems to have been taken by surprise by their opponents' amphibious capacity and seemed somewhat unnerved by the LVTs emerging from the water so that by daylight on 12 April all three columns had made some 4 miles headway, linking up in the Menate-Longastrino area. 169th Brigade then pushed forward on the road towards Filo and 167th Brigade continued up the Reno, rolling up the German defences as far as the confluence with the Santerno river to link with the Italian Cremona Combat Group which had advanced from the south.
Reacting to the Allied attack, von Vietinghof ordered 29th Panzergrenadier Division south to reinforce the Argenta gap. Its 15th Panzergrenadier Regiment arrived to reinforce 42nd Jaeger Division on 12 April but the rest of the division had been north of the Po and, delayed by air damage and fuel shortages was not in position until 14 April.
Early on 13 April the 38th (Irish) Brigade, of 78th Battleaxe Division, attacked northward from Indian 8th Division's bridgehead across the Santerno river with the objective of seizing a bridgehead across the Reno at Bastia, in the mouth of the Argenta gap. Meanwhile, to their right, 56th Infantry Division launched the second phase of its operation, Impact Royal. This involved No. 9 Commando of 2nd Commando Brigade and 24th Guards Brigade advancing up the flooded margins of Lake Comacchio in LVTs to concentrate near Chiesa del Bando, 6 miles (9.7 km) north west of Menate and develop a threat to Argenta which lay some 3 miles to the south west of this objective.[A foothold was established on the Fossa Marina, a canal running roughly east to west from Argenta to the lake and a 1 mile short of their objective but then the newly arrived 15th Panzer Grenadier Regiment blocked further progress and an attempt to take the bridge across the Fossa on 14 April was beaten back.
In the morning of 14 April forward elements of 38th Brigade had crossed the bridge over the Reno at Bastia but had been forced back by an armoured counterattack. It was decided to confine immediate activity to mopping up south of the Reno and await the approach of 167th Brigade which, advancing on both banks of the Reno, would shortly threaten the flank of the defenders north of the river in Bastia and oblige them to retire. Rather than wait for the bridge at Bastia to be cleared, V Corps commander, Lieutenant-General Charles Keightley ordered 78th Division's 11th Infantry Brigade to use 56th Division's bridges over the Reno in order to get forward towards Argenta without delay.