One of the main anti-aircraft weapons used by the Fil-Am forces on Bataan was the 3-inch anti-aircraft gun. It was the standard medium caliber AA weapon at the start of the war. Shown here is a 3-inch Gun M3 (adopted for service in 1928) of the Anti-Aircraft Command. It is emplaced on a Mounting M2A1 (differed from the Mounting M2 by carrying the spare wheels on elevated mounts; developed in the mid-1930s).
This gun was a mobile system, meaning it was transportable, as evidenced by the detachable wheels and the prime movers in the background. The long outrigger arms folded up in the middle and then folded back to lie on the platform; this double-fold gave it the “Spider Mount” nickname. The perforated metal platform formed a working surface for the gun crew, and rotated with the gun. It could be folded up along with the outrigger arms into a traveling position for towing.
The M3 3-inch AA gun could hit an aerial target at a maximum horizontal range of 14,780 yards and could reach just below a 10,000-yard ceiling, firing its 12.87-pound HE rounds at up to 25 rounds per minute. The same gun was initially used in shipboard and ground installations and used the same ammunition as the M5 3-in. anti-tank gun. As with other AA artillery, the gun could be used against ground targets when the tactical situation called for it.
Gun configuration information from Ian V. Hogg’s “Anti-Aircraft Artillery,” The Crowood Press, 2002, pp 86-87.
Weapon performance information from: “M3 3-inch Anti-Aircraft Artillery,” at: http://olive-drab.com/idphoto/id_photos_3in_aaa.php