▁ranks ▁and ▁ 1 9 ▁A TS , ▁which ▁was ▁formally ▁part ▁of ▁the ▁Group ▁signal ▁unit . ▁ ▁Operation ▁D iver ▁ ▁The ▁Luft wa ffe ▁began ▁a ▁new ▁bomb ing ▁campaign ▁against ▁London ▁in ▁early ▁ 1 9 4 4 ▁( the ▁Baby ▁Bl itz ). ▁ ▁By ▁now ▁the ▁night ▁f ighter ▁def ences , ▁the ▁London ▁Inner ▁Art illery ▁Zone ▁and ▁Th ames ▁Est u ary ▁def ences ▁were ▁well ▁organ ised ▁and ▁the ▁attack ers ▁suffered ▁heavy ▁losses ▁for ▁relatively ▁small ▁results . ▁More ▁significant ▁were ▁the ▁V - 1 ▁flying ▁bomb s , ▁c oden amed ▁" D ivers ", ▁which ▁began ▁to ▁be ▁launched ▁against ▁London ▁from ▁northern ▁France ▁soon ▁after ▁D - Day . ▁These ▁presented ▁AA ▁Command ' s ▁biggest ▁challenge ▁since ▁the ▁Bl itz . ▁Def ences ▁had ▁been ▁planned ▁against ▁this ▁new ▁form ▁of ▁attack ▁( Operation ▁D iver ), ▁but ▁it ▁presented ▁a ▁severe ▁problem ▁for ▁AA ▁guns . ▁Anti - air craft ▁g unn ers ▁found ▁that ▁such ▁small ▁fast - mov ing ▁targets ▁were ▁very ▁difficult ▁to ▁hit . ▁The ▁cru ising ▁alt itude ▁of ▁the ▁V - 1 , ▁between ▁, ▁was ▁just ▁above ▁the ▁effective ▁range ▁of ▁light ▁anti - air craft ▁guns , ▁and ▁just ▁below ▁the ▁optim um ▁eng agement ▁height ▁of ▁heav ier ▁guns . ▁The ▁alt itude ▁and ▁speed ▁were ▁more ▁than ▁the ▁rate ▁of ▁traverse ▁of ▁the ▁standard ▁British ▁Q F ▁ 3 . 7 - inch ▁mobile ▁gun ▁could ▁co pe