Just saw a show on the tube yesterday, where a woman had driven her car into the river and as it was sinking she called 911.
The advice given to viewers - when you are in a sinking car, get outta there asap. Don't depend on having an air pocket, there may not be one or if there is, in your disoriented state you may never find it, also, you cannot open a car door when it's completely submerged, try to lower a window, which probably will not work either.
They showed a punch device available for less than $10, that will break a window easily.
That device is called a spring punch. They are always within reach in my shop anywhere near a machine tool.
They work great for punch starting drill holes.
They also work great for breaking windows.
I trained my daughters to have one with them in the center console...
Recently, my younger daughter 'splained that a .40 does a great job on a window as well, and it's multi-purpose.
Yeah... she's the one that scored expert with grenades. Loud boom=good in her book. Go figure. I raised practical children. ;)
/johnny
I'd tell you what it is about senility that I hate, if I could just remember what it is.