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How It Worked

May 2024
1min read



The external shape [resembled] two tortoise sheik of equal size joined together… . The entrance was elliptical … so small as barely to admit a person …


A brass cover, resembling a hat with its brim and crown, shut water-tight … and was hinged to turn over sidewise when opened.… There were … several small glass windows in the crown, with covers to secure them.


The vessel is chiefly ballasted with lead [making it] so stiff that there was no danger of oversetting. About two hundred pounds … would be let down forty or fifty feet below the vessel; this enabled the operator to rise instantly to the surface … in case of accident.


[The boat moved horizontally] by an oar … formed upon the principle of the screw, fixed in the forepart of the vessel … turned by hand or foot … [and moved vertically by] an oar placed near the top of the vessel.


[A] rudder, hung to the hinder part of the vessel might be used for rowing forward. Its tiller was … at the operator’s right hand, fixed at a right angle to an iron rod which passed through the side of the vessel…. Raising and depressing the … tiller turned the rudder …


[Depressing a brass foot-valve admitted water into the bottom of the vessel and] two brass forcing pumps … at each hand [ejected it] … the water rose [in the depth gauge] … bearing the cork, with its phosphorous, on its surface … [so] the depth of the vessel under water … [could be] ascertained by graduated lines.


The inside [contained] air sufficient to support [the operator] thirty minutes without receiving fresh air. There were two air pipes in the crown. A ventilator within drew fresh air through one … and discharged it into the lower part of the vessel; [this] expelled impure air through the other… . Both … shut themselves off whenever the water rose near their tops … and opened themselves immediately after they rose above the water.


[In] the forepart of the brim of the crown was a … wood-screw … by pushing the wood-screw up against the bottom of a ship and turning it at the same time, it would enter the planks; when the wood-screw was firmly fixed, it would be cast off by unscrewing the rod, which fastened it upon the top of [its] tube.… [A] powder magazine made of two pieces of oak timber, large enough when hollowed out to contain 150 pounds of powder … was secured in its place by a screw turned by the operator. A strong piece of rope [bound] the magazine to the wood-screw… . Within the magazine was an apparatus, constructed to run any proposed length of time under 12 hours; when it had run out its time, it unpinioned a strong lock resembling a gun-lock, which gave fire to the powder. This apparatus was so pinioned that it could not possibly move till, by casting off the magazine … it was set in motion.

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