If conditions were favorable for invasion the warning order ‘Stand To’ would be issued. It did not require any action on Emergency / Invasion committees or Home Guard with the exception that they should ensure emergency arrangements were ready to put into immediate operation.
If invasion was imminent, the warning order ‘Action Stations’ would be issued. The Home Guard would be called out and civil arrangements for feeding them would come into operation.
Invasion was split into four phases which determined the help the military could give to the civil population:
Phase A (In the event of a large scale bombing attack under immediate threat of invasion) - military could give every assistance in clearing roads of debris etc.
Phase B (When the invasion has begun but the enemy is some distance away) - only limited assistance could be given.
Phase C (When battle is taking place locally or is imminent) - no assisatance could be given as military would be fully manning defences.
Phase D (Enemy in temporary occupation of neighbourhood)
The following Alarm signals were the only ones permitted:
• Siren – national signal for ‘Alert’ and ‘Raiders Passed’.
• Wardens Whistles – incendiary bombs falling.
• Church Bells – warning for the landing of airborne or parachute troops. Warning was not to be used for seaborne landings.
• Rattle – military or civil warning for gas.
When invasion was in progress, although the fighting not in the vicinity of the local town or parish (Phase A and B), the civil community should still be expected to be isolated as normal communications and arrangements broke down. The Emergency / Invasion committee would have to ensure emergency arrangements (e.g. food distribution) were put into operation.
If the fighting reached the local community or the enemy occupied the area (Phase C and D), the Emergency / Invasion Committee would coordinate emergency arrangements and help and guide the civil population.