'Public Warning', aircraft recognition poster, 1915.

Poster printed for HMSO by Sir Joseph Causton and Sons Ltd, London, showing silhouettes of German and British airships and aeroplanes. These recognition guides were posted as public information and to asist observers in reporting enemy aircraft. World War I was the first conflict in which aircraft were used to drop bombs on enemy targets. Early attempts were limited and crude, but in 1915 the Germans began organised bombing raids using Zeppelin airships. By 1917 London was suffering regular air raids by Gotha bomber aeroplanes by day and night, with numerous casualties on the ground. By the end of the war, both sides had long-range heavy bomber aeroplanes capable of delivering substantial payloads of bombs deep into enemy territory.