Other commonplace uses of sapphire in everyday life include semiconductors and barcode sensors, where the material is again chosen due to its ruggedness.
Sapphire has also found widespread use in is the avionics world, where its ability to withstand extreme high and low temperatures — along with its resistance to damage — makes it a useful tool for the aviation displays in aircraft. Another regular application is in the optic heads of missiles. These missiles are regularly equipped with a combination of infrared, radar, and optical sensors for guidance, and the optic heads need to remain undamaged when the missile is moving through the air, or else being handled on the ground. Sapphire is also used in some iterations of bullet proof glass.
Sapphire is second only to diamond for hardness. You can take a handful of sand and use it to clean the lens. Goodbye screen protector film! Lol! I have no idea what the impact strength is though as I never whacked it with a hammer. Optically though, sapphire is awesome with low distortion. The instruments were pushing about the equivalent of about 2 megawatt per cm2 with a beam a few tenths of a micron diameter beam. Believe me, optical distortion of any significant amount would have been detectable.
BTW, no proprietary info in these descriptions. Sapphire has been used in industrial optics for years for its unmatched scratch resistance and other info is in public domain literature.