The first Gatling gun was invented and built by Richard Jordan Gatling, of Indianapolis, Indiana, in 1862. The gun was test-fired many times for representatives of the U.S. government and for representatives of foreign governments. The weapon was patented on May 9, 1865. The gun was subject to a variety of problems, including jamming, and was modified at Cooper's Firearms Manufactory in Philadelphia, Pennsylvania, and subsequently at Colt's Armory in Hartford, Connecticut.
The basic idea of the gun is that there are series of barrels, which revolve inside of a supporting frame. As the barrels revolve, a mechanism automatically inserts rounds being fed from a vertical magazine mounted atop the gun. As the barrels continue to revolve, each barrel is cocked, fired and the shell casing removed in one single revolution. The barrels are revolved through the use of a crank mounted on the weapon.
The Gatling gun saw its first major action in the Spanish-American War of 1898. The most famous use of the Gatling gun was at San Juan Hill. Here, as the infantry ascended San Juan Hill, "a peculiar drumming noise was heard." Some thought it was Spanish machine guns. Theodore Roosevelt, on the adjacent Kettle Hill, yelled to his men "Its the Gatlings, men, our Gatlings!". He was right, Lieutenant Parker was bringing his four Gatlings into action, and shoving them nearer and nearer the front. Parker himself later recorded the following account of the event:
"The guns were pushed right up in the hottest place there was in the battle-field...and put into action at the most critical point of the battle... [the guns] so successfully subdued the Spanish fire that from that time to the capture of the practically impregnable position was only eight-and-one-half minutes. The expenditure of ammunition during this time, in which a continuous fire was kept up from three guns, was 6,000 rounds per gun..."
This action represented the first time that the U.S. Army used close-support machine guns in an attack against an enemy position. The event would have ramifications for years to come.
During the late 1890s, Mr. Gatling attached an electric motor to a few experimental models. Those models achieved a rate of fire that exceeded 3,000 shots per minute, a far cry from the original 200 shots per minute. But, alas, the gun was declared obsolete in 1911.
The ideas behind the Gatling Gun then went unused until the 1950s, when someone realized that the machine guns of the day had rates of fire slower than most models of the original Gatling Guns. Arms designers then developed the Vulcan, and later the Avenger guns, both of which use most of the basic principles of the original Gatling gun.
Please be respectful of those who rest near the cache. There is no need to climb or otherwise disturb anything. The .40 caliber cache is in plain sight, if you are looking from the right angle. Good luck.