▁or ▁pressure ▁on ▁the ▁g unn ers ▁shoulder ▁rest ▁over coming ▁the ▁fr iction ▁in ▁the ▁mechanism . ▁De pression ▁and ▁elev ation ▁of ▁the ▁gun ▁was ▁either ▁through ▁a ▁ge ared ▁mechanism ▁or , ▁with ▁the ▁g ears ▁dis eng aged , ▁free ▁through ▁movement ▁of ▁the ▁gun ner ' s ▁shoulder ▁rest . ▁ ▁Vari ants ▁ ▁M 2 A 1 ▁( 1 9 3 5 ). ▁Initial ▁production ▁type ▁with ▁single ▁fixed ▁tur ret ▁containing ▁one ▁. 5 0 ▁cal ▁machine ▁gun . ▁Se vent een ▁units ▁were ▁produced . ▁M 2 A 2 ▁( 1 9 3 5 ). ▁T win ▁tur rets ▁with ▁single ▁. 5 0 ▁machine ▁gun ▁in ▁each ; ▁the ▁tur rets ▁partly ▁ob struct ed ▁each ▁other ▁limit ing ▁fields ▁of ▁fire . ▁Dub bed ▁" M ae ▁West ". ▁ 2 3 9 ▁units ▁produced ▁from ▁ 1 9 3 6 – 3 7 . ▁M 2 A 3 ▁( 1 9 3 8 ). ▁T win ▁tur rets ▁with ▁two ▁machine ▁guns , ▁th icker ▁arm or , ▁slightly ▁length ened ▁h ull , ▁improved ▁engine ▁access , ▁increased ▁g ear ▁r ati os , ▁better ▁engine ▁cool ing , ▁improved ▁susp ension , ▁and ▁other ▁minor ▁detail ▁changes . ▁ 7 2 ▁units ▁produced . ▁M 2 A 4 ▁( 1 9 3 9 ). ▁Single ▁tur ret ▁with ▁ 3 7 mm ▁gun . ▁Th icker ▁arm or . ▁ 3 7 5 ▁units ▁produced . ▁Or ders ▁went ▁to