 The Thames possessed several naval installations of great importance, including the victualling yards at Deptford, the armaments works of Woolwich Arsenal, the shipbuilding yards at North Woolwich, and the magazines at Purfleet.It was not possible for large warships to reach central London, as the river was not yet deep enough to take ships of more than 400 tons above Deptford.As the American Civil War soon showed, it was quite possible for the warships of the day to run past forts and attack up coastal rivers.