Superstition

Pat was absolutely right in her answer - the first light drew the attention of the sniper, the second he took aim and the third he fired. Some accounts date the superstition back to the Boer War but apparently it became widespread during the trench warfare of World War I.

There are just as many superstitions in the forces as elsewhere. One of my favourites is that it's considered extremely bad luck to mention the word 'Rain' when on exercise or operations unless it is actually raining.