Peckham, South London, UK, 1939. Local lads (posing in their new gas-masks) assisting their neighbours in the erection of an Anderson air-raid shelter. In April, 1939, just before the start of World War 2 on September 1, the government began distributing to the civilian population 3.5 million Anderson shelters.They were instructed to erect the six galvanised steel panels within two months. This decision, together with the issuing to every civilian of the General Service Respirator(gas mask), resulted from the German strategy of terror-bombing urban centres without regard to civilian casualties. A notable example was the attack from the air on Guernica during the Spanish Civil War. There was also a fear of chemical warfare such as the German use in World War 1 of poisonous gases: chlorine gas, mustard gas, and phosgene as weapons.