 The drive for Trun by Polish and Canadian Armoured Divisions began on 16 August , with preliminary attacks in preparation for an assault against Trun and Chambois . On 17 August , both armoured divisions of the Canadian 1st Army advanced . By early afternoon , the Polish 1st Armoured Division had outflanked the 12th SS Panzer Division , enabling several Polish formations to both reach the 4th Armoured Division 's objectives and significantly expand the bridgehead northwest of Trun . Stanisław Maczek — the Polish divisional commander — split his forces into three battlegroups each of an armoured regiment and an infantry battalion . One of these struck southwest , cutting off Trun and establishing itself on the high ground dominating the town and the Dives river valley , allowing for a powerful assault by the Canadian 4th Armoured Division on Trun . The town was liberated on the morning of 18 August . 
