Corning supplied thick windows of fused silica to protect optical elements on submarine periscopes. The Polaris missile program (1961-1996) used nuclear-powered submarines to launch missiles from within the water. Fused silica was able to resist the extreme pressure of ocean depths.
Corning began using fused silica to make submarine periscope head windows for the United States Navy, certifying fused silica as a sub-safe material. Corning has also supplied fused silica for submarine port windows.