These days, when we discuss the threat posed by the river Thames, we tend to be talking about flooding. Back in the early days of The Engineer, London feared a far more tangible foe: the foreign naval forces that might use the river to attack the capital.
Reporting on a meeting at the ’London Tavern’ that discussed ’the best means for securing efficient protection to the great interests and immense wealth of the metropolitan district’, The Engineer broached a proposal for an ’impregnable iron fortress’.
’A model and several drawings, plans and sections of Mr JW Hall’s fortress, to be erected if approved of at the Nore, were exhibited,’ reads the article. ’The proposed fortress is to be in the shape of a round tower, diminishing in diameter towards the summit at the rate of 1in to the foot. It is to be 235ft high and 126ft in diameter at the base. An air shaft, 20ft in diameter, runs from top to bottom. A spiral staircase is constructed around this shaft, leading to 11 floors or compartments, each having 32 windows and a door. At the top is the sleeping room, the next floor is the officers’ mess room. One compartment is devoted to the steam engine, boiler and six life boats.
There is also a room appropriated to shot and shell and the powder magazine is placed below the water mark. There is to be a lighthouse at the top, 12ft in diameter, which can be raised or lowered by a telescope slide as the circumstances of peace or war may require.’ Finally, the article reported on an ingenious steam-powered system that doubled as central heating and an intruder deterrent: ’The air shaft is surrounded by 12 hollow iron columns to support the floors and heat the rooms by steam, which the inventor also proposes to use as a means of scalding an unwelcome visitor.’
There appears to be no record of Hall’s iron fortress being constructed, but the idea was revisited during the Second World War when a series of army forts was built in the Thames estuary. The rusting Maunsell sea forts (pictured) are still standing today.