Reveille (British and Canadian English: [ɹəˈvæ.li]; American English: [ˈɹɛ.və.li]) is most often associated with the military; it is chiefly used to wake military personnel at sunrise. In modern times the US military plays (or sounds) Reveille at 6:00 am. The actual song is more or less traditional rather than useful in modern times. For example, on most US military bases, the headquarters staff will sound Reveille along with a cannon shot as the American flag is raised in the morning. All military personnel upon hearing the music on loudspeakers throughout the base will "face the music," as it were, and render a hand salute. Canadian English is the form of English language used in Canada, spoken as a first or second language by over 25 million – or 85 percent of – Canadians (2001 census). ... American English (AmE) is the dialect of the English language used mostly in the United States of America. ... Sunrise over the sea Sunrise, also called sunup in some American English dialects, is the time at which the first part of the Sun appears above the horizon in the east. ... The armed forces of the United States of America consist of the United States Army United States Navy United States Air Force United States Marine Corps United States Coast Guard Note: The United States Coast Guard has both military and law enforcement functions. ... The 12-hour clock is a timekeeping convention in which the 24 hours of the day are divided into two periods called ante meridiem (AM, Latin for before noon) and post meridiem (PM, Latin for after noon). Each period consists of 12 hours numbered 12, 1, 2, 3, 4, 5... Flag ratio: 10:19 Stars and stripes redirects here. ...

In Indian Army the Reveille is sounded at 6am (or sun rise), and the regimental colours are hoisted. The P.T (Physical Training parade) also starts immediately, so that means that soldiers for all practical reasons would have to get up much before that.

In Britain, it is often used to mark the end of the period of silent reflection at Remembrance Day and Remembrance Sunday services. Wreaths of artificial poppies used as a symbol of remembrance Remembrance Day or Armistice Day is a day of commemoration observed in the Commonwealth of Nations and various European countries (including France and Belgium) to commemorate World War I and other wars. ... In the United Kingdom Remembrance Sunday is the Sunday nearest to 11 November - Remembrance Day, which is the anniversary of when hostilities in the First World War ended at 11 a. ...

It is an interesting song because it can be played with any combination of valves (or all open valves). Probably due to the fact that it was first played on a bugle, that lacks valves, and was played by altering the embouchure.