▁anti - air craft ▁role , ▁especially ▁in ▁naval ▁use . ▁His p ano ▁introduced ▁a ▁number ▁of ▁mount ings ▁with ▁a ▁variety ▁of ▁sight ing ▁systems , ▁fe eds ▁and ▁power ▁traverse . ▁The ▁H S . 6 3 9 - B 3 ▁( l ater ▁known ▁as ▁the ▁G AI - CO 1 ) ▁was ▁a ▁single - gun ▁mount ing ▁fed ▁from ▁a ▁ 7 5 - round ▁drum , ▁a ▁fairly ▁serious ▁limitation ▁for ▁a ▁gun ▁with ▁such ▁a ▁high ▁rate ▁of ▁fire . ▁Vari ants ▁included ▁the ▁H S . 6 3 9 - B 4 ▁( GA I - CO 3 ) ▁with ▁a ▁ 5 0 - round ▁drum ▁mounted ▁on ▁top ▁of ▁the ▁weapon , ▁and ▁the ▁H S . 6 3 9 - B 5 ▁( GA I - CO 6 ) ▁that ▁used ▁dual ▁ 7 5 - round ▁mag az ines ▁for ▁longer ▁firing ▁times . ▁The ▁H S ▁ 6 6 5 ▁was ▁a ▁triple - mount ▁variety ▁using ▁the ▁same ▁drum ▁fe eds . ▁The ▁H S . 6 6 6 A ▁( GA I - DO 1 ), ▁developed ▁in ▁the ▁mid - 7 0 s , ▁featured ▁two ▁H S . 8 2 0 ▁with ▁new ▁ 1 2 0 - round ▁box ▁mag az ines ▁mounted ▁on ▁a ▁shared ▁hyd ra ul ically ▁power ed ▁platform ▁which ▁could ▁be ▁tied ▁into ▁an ▁associated ▁rad ar - gu ided ▁fire - control ▁system . ▁ ▁After ▁O er