In the days of cannon, it took as long as twenty minutes to load and fire a gun. When a ship fired her guns in salute, she rendered herself powerless for the duration. By emptying their guns, the ship's crew showed shore batteries and forts that they were no threat. Over time, this gesture became a show of respect, with both shore and ship gun batteries firing volleys.
When president is honoured with 21 gun salute, most Navies provide gun salutes for naval officers on significant occasions, using the following protocol:
- Admiral-17 guns
- Vice Admiral-15 guns
- Rear Admiral (upper half)-13 guns
- Rear Admiral (lower half)-11 guns
All gun salutes are fired at five second intervals. Gun salutes will always total an odd number.