As the 7.5 mm Reibel machine gun was only effective against the lightest armour at a very short distance because its AP-bullet could just penetrate eight millimetres of armour at fifty metres, several efforts were made to provide some more serious antitank-capacity to AMR units. The first was to uparm the main production run vehicles with a heavier machine-gun. The second was to fit the vehicles with the 25 mm antitank-gun; to this effect both a tank (the ZT 2) and a self-propelled gun (the ZT 3), were developed. The 25 mm gun vehicles were primarily intended for the reconnaissance units, the "Groupes de Reconnaissance de Division d'Infanterie", of the motorised infantry divisions; these were part of the Infantry, but the Cavalry provided the reconnaissance elements. On 22 July 1936 it was decided to assign four of such 25 mm vehicles to each GRDI. The decision to design two types, despite the very small production batches, was motivated by the desire to let them operate in pairs; the low inconspicuous self-propelled gun would directly ambush enemy vehicles and the higher tank, fitted with a radio set, would be more behind in an oversight position, also with its rotatable turret covering the flanks.