 On 6 June 1944 , the British 6th Airborne Division was given the task of securing the left flank of the Allied <unk> landings . One of their objectives was the destruction of the Merville Gun Battery . Allied planners had judged from the size of the concrete gun emplacements that the guns must be around 150 mm in calibre . If so , the guns would have a range of about 8 miles ( 13 km ) and could threaten Sword Beach , to the west of <unk> , where the 3rd British Infantry Division were due to land later that day . 
