The tradition of rendering a salute by cannon originated in the 14th century as firearms and cannons came into use. Since these early devices contained only one projectile, discharging them rendered them harmless.
Initially, the tradition began as a custom among ships, whose captains had volleys fired upon entering a friendly port to release its arsenal, which demonstrated their peaceful intentions (by placing their weapons in a position that rendered them ineffective.)
This custom was eventually adopted by the British navy whose ships fired seven-gun salutes, choosing the number seven because it was thought to be the luckiest of the odd numbers.
And, it was thought seven was also selected because of its astrological and Biblical significance. Seven planets had been identified and the phases of the moon changed every seven days.
The Bible states that God rested on the seventh day after Creation, that every seventh year was sabbatical and that the seven times seventh year ushered in the Jubilee year.
Land batteries, having a greater supply of gunpowder, were able to fire three guns for every shot fired afloat, hence the salute by shore batteries was 21 guns.
As time went on, gun salutes continued to be fired in odd numbers, due to the fact that ancient superstitions held that uneven numbers were lucky. (Even as far back as 1865, firing of an even number of guns in salute was taken as an indication that a ship’s captain, master or master gunner had died on the voyage.)
The US Navy regulations for 1818 were the first to prescribe a specific manner for rendering gun salutes (although gun salutes were in use before the regulations were written down).
Those regulations required that “When the President shall visit a ship of the United States’ Navy, he is to be saluted with 21 guns.” (It may be noted that 21 was the number of states in the Union at that time.)
For a time thereafter, it became customary to offer a salute of one gun for each state in the Union, although in practice there was a great deal of variation in the number of guns actually used in a salute.
After 1841, it was customary for a US president to receive a 21-gun salute, with the vice president receiving 17. Today, however, the vice president receives 19.
On Aug. 18, 1875, Great Britain and the United States announced an agreement to return salutes, “gun for gun,” making the 21-gun salute the highest national honor.
In 1890, regulations designated the “national salute” as 21 guns and redesignated the traditional Independence Day salute, the “Salute to the Union,” equal to the number of states. Fifty guns are also fired on all military installations equipped to do so at the close of the day of the funeral of a President, ex-President, or President-elect.
The 21-gun salute became the highest honor a nation rendered.
Today, the national salute of 21 guns is fired in honor of a national flag, the sovereign or chief of state of a foreign nation, a member of a reigning royal family, and the President, ex-President and President-elect of the United States. (Senator Daniel Inouye was given a 19-gun cannon salute.)
It is also fired at noon of the day of the funeral of a President, ex-President or President-elect, on Washington’s Birthday, Presidents Day and the Fourth of July. On Memorial Day, a salute of 21 minute guns is fired at noon while the flag is flown at half-mast.
In Hawaiʻi, “King Kalākaua, the Queen, and the national flag were accorded a 21-gun salute, an ambassador extraordinary and plenipotentiary rated 19 guns, a governor or high commissioner 17, an admiral of the fleet 15, a minister resident 13, a charge d’affaires 11, a consul general nine, and a consul seven.” (Schwieizer)
While King Lunalilo was on his deathbed, he requested a burial at Kawaiahaʻo Church, with his mother on the church’s ground. He wanted, he said, to be “entombed among (my) people, rather than the kings and chiefs” at Mauna ʻAla (Royal Mausoleum) in Nuʻuanu Valley.
Lunalilo died February 3, 1874; during his funeral procession, eyewitnesses reportedly stated that a sudden storm arose, and that twenty-one rapid thunderclaps echoed across Honolulu which came to be known as the “21-gun salute.” (RoyalOrderOfKamehamehaI-org)
While the sum of the digits in 1776 adds up to 21, reportedly there is no historical link to the year of our nation’s signing of the Declaration of Independence and the 21-gun salute.
The image shows the Kaka‘ako Saluting Battery and flagstaff (Hammatt) 1887. In addition, I have added other related images in a folder of like name in the Photos section on my Facebook and Google+ pages.