▁ 4 4 7 , ▁ 4 4 8 ▁and ▁ 4 4 9 ▁S / L ▁Comp an ies ▁at ▁Br istol . ▁ ▁It ▁formed ▁part ▁of ▁ 4 6 th ▁Anti - A ircraft ▁Brigade ▁in ▁ 5 ▁AA ▁Division . ▁The ▁brig ade ▁commanded ▁the ▁' B rist ol ▁Def ended ▁Area ', ▁including ▁potential ▁targets ▁such ▁as ▁Av on mouth ▁D ock s ▁and ▁the ▁Br istol ▁Aer op lane ▁Company ▁factory ▁at ▁Fil ton ▁Aer od rome . ▁ ▁World ▁War ▁II ▁ ▁M obil isation ▁and ▁Ph oney ▁War ▁ ▁In ▁February ▁ 1 9 3 9 ▁the ▁existing ▁AA ▁def ences ▁came ▁under ▁the ▁control ▁of ▁a ▁new ▁Anti - A ircraft ▁Command ▁and ▁In ▁June ▁a ▁partial ▁mobil isation ▁of ▁T A ▁units ▁was ▁begun ▁in ▁a ▁process ▁known ▁as ▁' cou vert ure ', ▁where by ▁each ▁AA ▁unit ▁did ▁a ▁month ' s ▁tour ▁of ▁duty ▁in ▁rotation ▁to ▁man ▁selected ▁AA ▁and ▁search light ▁positions . ▁On ▁ 2 4 ▁August , ▁ahead ▁of ▁the ▁declaration ▁of ▁war , ▁AA ▁Command ▁was ▁fully ▁mobil ised ▁at ▁its ▁war ▁stations . ▁ ▁In ▁the ▁near - total ▁absence ▁of ▁light ▁AA ▁( LA A ) ▁guns , ▁det ach ments ▁from ▁other ▁units ▁were ▁deployed ▁with ▁Lewis ▁guns ▁( L G s ) ▁during ▁October ▁and ▁November ▁ 1 9 3 9 ▁to ▁cover ▁various ▁Royal ▁Air ▁Force ▁( RA F ) ▁air fields ▁and ▁aircraft ▁fact ories ▁designated ▁as ▁V ul