Gallery 3 · Beneath the Surface
Diving Helmet, Twelve-Bolt
Siebe Gorman & Co., London, c. 1935
Spun copper, brass, glass
Divers wearing helmets like this one repaired the harbour walls and cleared wrecks from the channel. Air was pumped down to them by hand from a boat above, and the only way to talk to the surface was by tugging a rope.
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The helmet was bolted to a canvas diving suit with twelve brass bolts, which is where its name comes from. Together with lead boots and weights, the full outfit weighed around eighty kilos.
Air came in through the fitting at the back of the helmet and escaped through a valve the diver controlled with his head. Too much air and he floated to the surface; too little and the pressure of the water squeezed the suit tight.
Signals were simple: one pull on the line meant 'I am all right', two meant 'give me more rope', and four meant 'pull me up now'.