This is a bugle call played by military forces to wake up the troops at the start of the day. As such it serves a similar purpose to a variety of other bugle calls used by UK and other forces around the world, such as Rouse, The First Post, Reveille (UK) or Reveille (US). Calls such as The Last Post and Taps are played at the end of the day. See the links at the left to download the sheet music or audio files. More bugle calls are listed in our article about the history and cultural impact of Bugle Calls
The image below is the first page of the sheet music, and here you can download the full sheet music for Charlie Reveille (bugle call) in PDF format.