This ordinance wrench, in less than perfect shape, was picked up this afternoon.  It is 8 7/8 inches long, and 1/2 inch thick.  It has deeply stamped identifications on it - 4 INCH S.T.M. and FIRING PIN. The end of the wrench has been bent down into a screwdriver. There is shallower stamped logo which I take to mean Ordnance, but I may be wrong. I served in the U.S. Army's Quartermaster Corps.  Can anyone shed some light on this tool?

I picked up 3 or 4 similar wrenches last year that have 3 Inch SIM on them.  I could not find very much information on the internet, but I think they may have gone to secondary battery guns (3 inch) on a British warship, possibly a destroyer.

SIM is MILspeak (1970's) for Surface to air Intercept Missle, it would be relatively small..
(SIM's were to shoot down the other fellows' SAM's)
All I could find for STM is Supersonic Tactical Missle, sounds large.....

There is a plethoria of weapons systems for battleships in the 50's or so when the old war ships were being retrofitted, and all kinds of weird shortlived systems were tried, most with the usual weird acronyms...

STM in the British Navy stands for Ship's Technical Manual, and was used in conjunction with Mark IV ship's guns.  I don't know if this ties in with this wrench, or is just a coincidence of no import.

My wrenches have Mark I and Firing Pin on them.  I have one listed on Ebay.  If you put Mark I 3 inch SIM into the search engine, it will come up if you want to look at the pics and compare it to your wrench.