Someone brought a blade in, and I finally deciphered the “S” from the tang stamp, with help of the www. Evidently, Imperial decided to use up a bunch of leftover M-7 bayonet blades, and put a cross-guard with screwdrivers, and and nail-pulling-claw buttcap, on them.
Anyway, I’m guessing that this one met its demise by being used to actually hammer on something. (The rolling on the tang indicates hammering, rather than nail-pulling.)
Also, the owner obviously didn’t like the saw-teeth on the spine. Can’t blame anyone for that! Good riddance.
Here is a link with a picture of the original item: http://bushcraftusa.com/forum/threads/imperial-m7s.68435/
The M7 bayonet was designed for, and introduced with, the M16 rifle in 1964.