ans ▁began ▁using ▁heavy ▁bom bers ▁against ▁the ▁city . ▁In ▁Germany , ▁a ▁black out ▁was ▁only ▁enfor ced ▁in ▁a ▁zone ▁ 1 5 0 ▁kilometres ▁( 9 3 ▁miles ) ▁behind ▁the ▁Western ▁Front . ▁ ▁World ▁War ▁II ▁During ▁World ▁War ▁II , ▁the ▁Air ▁Ministry ▁had ▁forec ast ▁that ▁Britain ▁would ▁suffer ▁night ▁air ▁bomb ing ▁attacks ▁causing ▁large ▁numbers ▁of ▁civil ian ▁cas ual ties ▁and ▁mass ▁destruction . ▁It ▁was ▁widely ▁agreed ▁that ▁navigation ▁and ▁target ing ▁would ▁be ▁more ▁difficult ▁if ▁man - made ▁lights ▁on ▁the ▁ground ▁could ▁be ▁ex ting u ished . ▁As ▁early ▁as ▁July ▁ 1 9 3 9 , ▁ ▁Public ▁Information ▁Le af let ▁No ▁ 2 ▁( part ▁of ▁the ▁Air ▁Ra id ▁Pre ca utions ▁( A . R . P .) ▁training ▁literature ) ▁war ned ▁of ▁the ▁need ▁for ▁popular ▁discipline ▁to ▁ensure ▁that ▁the ▁black out ▁reg ulations ▁were ▁fully ▁enfor ced ▁during ▁the ▁black out ▁periods . ▁ ▁Black out ▁reg ulations ▁were ▁im posed ▁on ▁ 1 ▁September ▁ 1 9 3 9 , ▁before ▁the ▁declaration ▁of ▁war . ▁These ▁required ▁that ▁all ▁windows ▁and ▁doors ▁should ▁be ▁covered ▁at ▁night ▁with ▁suitable ▁material ▁such ▁as ▁heavy ▁cur tain s , ▁card board ▁or ▁paint , ▁to ▁prevent ▁the ▁escape ▁of ▁any ▁g lim mer ▁of ▁light ▁that ▁might ▁aid ▁enemy ▁aircraft . ▁The ▁Government ▁ens ured ▁that ▁the ▁necessary ▁materials ▁were ▁available . ▁External ▁lights ▁such ▁as ▁street ▁lights