A viewport was an opening within a wall or bulkhead that allowed for a being to see through. Typically made from transparisteel, most viewports were usually, but not always, weaker than a wall of a starship, though could be as strong as that of a building. Viewports also came in many different styles, shapes and sizes, depending on the needs of the builder, the user and the expense for either one.
On worlds where high technology was still in its infancy, or if it was not economically-feasible to use transparisteel, then a form of glass made from silicate material (sand) was utilized as a substitute.
The viewport on Executor-class Star Dreadnoughts had a safety mechanism that, when broken, would reseal itself with a reinforced metal window to keep the ship pressurized. This metal window was stored under the viewport itself and would protract automatically upon breakage of the ship's outer transparisteel.
- Shadows of the Empire Sourcebook
- Millennium Falcon Owner's Workshop Manual
- Book of Sith: Secrets from the Dark Side