The mission Cochrane had recruited Cheshire for was the destruction of German V3 long-range guns. As their third and potentially most destructive vengeance weapon, the Germans had constructed a pair of extremely large guns and positioned them in northern France. They were buried deep in underground bunkers near Mimoyecques in the Pas-de-Calais region. Once operational these powerful guns would be able to fire a shell into London every minute, and buried in the earth and protected by 50 feet of reinforced concrete, they were impervious to bombing attack. Such a target was far different than a marshaling yard. Area bombing the region where the guns were located would have no effect upon them.