The Glass Saw is a unique tool available only on the Victorinox Rescue Tool. It is used to saw through car windscreen/window safety glass.
There are a number of types of safety glass: shatterproof, hardened, laminated, coated etc. Laminated glass is usually used for car windscreens and has a layer of plastic 'sandwiched' between two sheets of glass. It does not shatter or fall apart, for instance when in a car accident, or when punched and broken with the window breaker. So this tool is used to saw through the glass once broken, so it can be removed.
It has another unique feature, compared to nearly all other Swiss Army Knife tools, in that it is replaceable. When it becomes dull it can be removed from the Rescue Tool and replaced with a separately purchasable replacement saw. This operation requires no special tools and is explained in the user manual.
Replacement saw part number: A8591
Note: This tool was previously incorrectly known as the disc-saw