ISO 21005 specifies how the properties must be of the glass for Marine windows and scuttles. In normal language, on ships the main issue is to keep water out, get light in and have a view to the outside. So the lower the windows are in the hull the thicker the glass has to be. To know how thick the glass must be in relation to the expected wave (water) pressure there is the ISO 614 standard.

Vetrotech Saint-Gobain Marine goes farther than ISO 614

The ISO 614 international safety standard concerns the use of tempered glass in marine applications. The standard describes the method for testing the pressure resistance of tempered glass. The safety glazing offered by Vetrotech already far outstrips this standard. In the event of breakage, every Vetrotech product will fall apart into blunt pieces of glass instead of dangerous, razor-sharp shards. Vetrotech means: extra safe!