The vehicle, developed and built by the White Motor Co., had a specially designed, commercial type truck chassis, surmounted by an armoured body.
Aside from its crew of two, it could transport 6 additional soldiers and had an armament of one M2HB cal. 50 and one M1919A4 cal. 30 Browning Machine Gun, both fixed on a skate rail leading all around the body's interior [see below].
Though not having the crossability, space and towing performance of the Halftracks, the M3A1 reached a total production of over 20,000 and saw service well beyond the war's end.
From 1942 on, the Soviet Union received almost 3,100 units of the Scout Car M3A1 and used it successfully as for reconnaissance duties, as command vehicle (e.g. General Rotmistrov) and for towing light artillery.
Towards the end of war it became as ubiquitous on the battlegrounds as the Jeep and the Dodge WC and, in the number of armour delivered to the Soviet Union, was surpassed only by the M4A2 Medium Tank »Sherman«.

Special thanks to Mr. Ron Perry, Netherlands, for providing indispensable detail shots on his web site.