National Geographic : 1965 Apr
533 To sink the wallowing SPID, a crew member pours lead pellets through a funnel and hose into its ballast tray. Five and a half tons of metal push the dwelling to the bottom. Bubbles trail the SPID as it descends below Sea Diver's dark hull. A diver checks watertight cases of equipment riding the ballast tray. Unique underwater lung, specially developed for the deep dive, permits Robert Stenuit to breathe and re-use a mixture of oxygen and helium through a purifying and recirculating system.