Several people involved in the development of early aircraft were aware of its potential to launch a long-range bombing attack deep inside enemy territory. In 1914 the Germans planned to send fleets of aircraft to bomb cities, factories and military installations in France and Britain. Only the German Zeppelin airship's could reach the targets deep in enemy territory, but there were only a few of them and they were extremely vulnerable to ground fire. Paris suffered regular raids during March 1915, and London experienced its first attack in May 1915.
The Russians had a few Sikorski 1M heavy bombers and the Italians had Caproni bombers, but both were fairly ineffective. By mid 1917 the German Gotha began long-range operations against Britain and France. Britain also developed new bombers such as the Handley Page and Airco DH-4.
Good anti-aircraft guns and fighter planes made it very difficult for bombers during daylight. When bombers were used at night they found it virtually impossible to find and hit specific targets. It was only after the end of the First World War that it became possible to carry out the policy of strategic bombing, envisaged by people like Hugh Trenchard, chief of staff to the RAF. It has been estimated that during the war, 254 metric tons of bombs were dropped from aircraft, causing over 9000 casualties.

Caproni Ca 101