4 1 ▁after ▁the ▁assembly ▁line ▁had ▁been ▁changed ▁over ▁to ▁the ▁M 3 . ▁ ▁Success or ▁vehicles ▁ ▁The ▁M 2 ▁light ▁tank ▁led ▁to ▁the ▁US ▁M 3 - series ▁and ▁M 5 - series ▁light ▁t anks . ▁The ▁Or dn ance ▁Department ▁viewed ▁the ▁M 2 A 4 ▁as ▁a ▁stop g ap ▁tank ; ▁work ▁to ▁improve ▁it ▁further ▁began ▁in ▁June ▁ 1 9 4 0 . ▁The ▁first ▁M 3 ▁Stuart ▁t anks ▁began ▁to ▁be ▁produced ▁in ▁March ▁ 1 9 4 1 ; ▁the ▁original ▁riv et ed ▁M 3 s ▁closely ▁res emble d ▁the ▁ ▁M 2 A 4 , ▁and ▁the ▁two ▁types ▁occasionally ▁served ▁in ▁the ▁same ▁units ; ▁an ▁easy ▁recognition ▁feature ▁was ▁the ▁rear ▁id ler ▁wheel . ▁On ▁the ▁M 2 A 4 , ▁the ▁id ler ▁was ▁raised ; ▁on ▁the ▁M 3 ▁it ▁tra iled ▁on ▁the ▁ground , ▁increasing ▁the ▁fl ot ation ▁of ▁the ▁heav ier ▁vehicle . ▁The ▁M 3 ▁retained ▁the ▁same ▁Cont inental ▁W - 6 7 0 ▁engine , ▁but ▁incorpor ated ▁ ½ - inch ▁th icker ▁( 1 ½ ▁in ch ▁total ▁thick ness ) ▁arm or ; ▁with ▁weight ▁increased ▁to ▁ 1 4 ▁tons . ▁The ▁tank ▁initially ▁kept ▁the ▁same ▁ 3 7   mm ▁gun ▁and ▁the ▁forward ▁firing ▁h ull ▁machine ▁guns , ▁but ▁the ▁tur ret ▁incorpor ated ▁improvements . ▁Event ually ▁over ▁ 4 , 5 0 0 ▁examples