ual ties ▁on ▁the ▁ground . ▁ ▁At ▁this ▁time ▁Th ames ▁South ▁had ▁a ▁planned ▁layout ▁of ▁ 2 5 ▁H AA ▁sites ▁( of ▁which ▁only ▁ 1 6 ▁were ▁occupied ), ▁controlled ▁from ▁a ▁Gun ▁Oper ations ▁Room ▁( G OR ) ▁at ▁Ch ath am . ▁It ▁ran ▁from ▁D art ford ▁to ▁Ch ath am , ▁where ▁there ▁was ▁a ▁strongly ▁def ended ▁area ▁containing ▁the ▁naval ▁dock y ards ▁at ▁Ch ath am ▁and ▁She ern ess ▁and ▁the ▁aircraft ▁factory ▁at ▁Ro chester . ▁ 2 8 ▁AA ▁B de ▁was ▁so ▁stretch ed ▁that ▁ 6 ▁AA ▁Division ▁gave ▁responsibility ▁for ▁L AA ▁cover ▁for ▁V ul ner able ▁Point s ▁( VP s ) ▁at ▁C ray ford , ▁North f le et , ▁Ro chester ▁and ▁the ▁Is le ▁of ▁Gra in ▁to ▁ 5 6 ▁L AA ▁B de . ▁The ▁search light ▁layout ▁in ▁Th ames ▁South ▁had ▁the ▁dual ▁role ▁of ▁assist ing ▁both ▁AA ▁guns ▁and ▁night ▁f igh ters . ▁As ▁the ▁Bl itz ▁continued , ▁the ▁number ▁of ▁H AA ▁guns ▁increased ▁and ▁they ▁became ▁more ▁effective : ▁an ▁average ▁of ▁ 2 0 , 0 0 0 ▁shell s ▁were ▁fired ▁each ▁German ▁bom ber ▁shot ▁down ▁in ▁September ▁ 1 9 4 0 ; ▁this ▁reduced ▁to ▁ 4 , 0 8 7 ▁in ▁January ▁ 1 9 4 1 ; ▁and ▁to ▁ 2 , 9 6 3 ▁shell s ▁per ▁kill ▁in ▁February