SOLID GLASS AND CERAMIC EXTERNAL-PRESSURE VESSELS,
  Serial No. NOW 63-0209-c-2, Ordnance Research Laboratory, Pennsylvania State University, University Park, PA, by J.D. Stachiw, January 1964, 72 page.

Solid glass or ceramic hulls provide the maximum buoyancy and internal useful volume for underwater vehicles. This material displays low creep characteristics and withstands external pressure cycling and mild underwater dynamic pressures. Scratches on the exterior surfaces do not decrease appreciably the compressive and elastic strength of such vessels when exposed to either static or cycling pressure. Connectors have been devised that enable glass cylinders to be joined into a monolithic structure that is resistant to both pressure and flexure.