What Is A Naval Salute Gun

In naval communication occasions, heads of state and government enjoy 21 salutes, naval marshals enjoy 19 salutes, admirals or officials of the same level enjoy 17 salutes, Rear Admiral 15, Rear Admiral 13, and Brigadier General 11.
Before the 20th century, British warships usually required the other country's warships to fire salutes when encountering or entering their ports. The common maritime etiquette is to determine the firing order based on the level of commanders of both fleets (or warships), and warships should first fire their guns to pay tribute when entering foreign ports.
It should be noted that both national and military salute guns use empty shells or specialized protocol ammunition. In history, some warships have fired empty guns on the high seas.