In the dual-purpose vehicle mount, the M2HB (heavy barrel) proved extremely effective in U. S. service: the Browning's . 50 caliber AP and API rounds could easily penetrate the engine block or fuel tanks of a German Bf 109 fighter attacking at low altitude, or perforate the hull plates and fuel tanks of a German half-track or light armored car. While the dual-purpose mounting was undeniably useful, it did normally require the operator to stand when using the M2 in a ground role, exposing him to return fire. Units in the field often modified the mountings on their vehicles, especially tanks and tank destroyers, to provide more operator protection in the anti-vehicular and anti-personnel role. The weapon was particularly hated by the Germans, whose attacks and ambushes against otherwise helpless stalled motor convoys were frequently broken up by . 50 caliber machine gun fire. Vehicles would frequently "recon by fire" with the M2 Browning, i. e. they would fire continuously at suspected points of ambush while moving through areas still containing enemy forces. One vehicle would fire exclusively to the right, the following vehicle to the left, the next one to the right, and so on in order to cover both flanks of the advancing convoy.