Prior to the use of the creeping barrage, artillery would fire on a set of primary targets for long periods, sometimes weeks, in order to "soften them up". Once the assault actually began, they would switch to secondary targets to avoid hitting their own troops with fire. In the creeping barrage some, or all, of the artillery was instead aimed just ahead of the advancing troops, carefully timed to continue moving forward with the advance.
First used by Bulgarians during the Adrianople siege in March 1913, the concept was not used in World War I until introduced by Sir Henry Horne for the Battle of the Somme in August 1916.