While the use of heavy Artillery Pieces and Batteries to protect a National Coastline is not a new application in warfare (a first use example dates to 1381 AD in Portugal), The then young United States realized very early that with a small Navy (and even smaller Army), it needed to likewise defend it's Coasts from possible Enemy attack. In 1794, The US Army was tasked with creating such a defensive Force, named The US Coastal Artillery Corps.
At first, The Coastline of The United States extended from only it's Eastern Seaboard, downward to The Southern Coast. Florida was still (in small part), Spanish Territory as was Colonial France, still in control of a portion of The Gulf of Mexico and then Louisiana. With acquisition of both Territories, The US had more than doubled their need to provide protection.
The War of 1812 between The US and Britain showed many flaws with American Coastal defense, in particular the size of such Cannon needed to engage a hostile Naval Force. After The War, The US increased it's Coastal Fortifications and Sea Batteries. This would be telling as well when The American Civil War began in 1861. The Conflict found much of The Southern Coastal Batteries in ''Rebel'' Control. Still, the effectiveness of The Union Naval Blockade also showed flaws which would be corrected by the 1890s.
The Spanish-American War of 1898 saw a rapid increase of Coastal Artillery Battalions (which now included The Western Coast.). The Coastal Artillery would become a major component within The US Army in 1907. They would be manned well into the 1940s. However, technology and the ''Face of War'' would change in 1945 with the development of Atomic Weapons. As such, the need for Coastal Defense waned, with many of the Forts closing and it's Force re-purposed (1950s). The growth of The US Navy and Air Forces would further fill the void.
The US Coastal Artillery used a wide variety through it's career (based on The Era). Mostly, the heaviest and most powerful of calibers were employed in Batteries. Typically, a Battery could range from as little as (4) Guns to as many as (8). Anti-Aircraft Batteries (WWI and II), were also commonly referred to as Coastal Artillery.
Most Batteries were considered Garrisons, as they also manned Coastal Forts. These Garrisons and Support Troops ranged from 100 to several thousand (during The Civil War). The Soldiers were all US Army, and identified themselves with their own distinctive insignia. This was a brace of crossed 19th Century Artillery Cannons (the traditional symbol of The Artillery). An Oval was placed over the bisection of the Guns, into which was placed a single Large Caliber Artillery Shell. The entire insignia was Brass (Gold), with the exception of The Center Oval, which was a Red Field with a Gold Shell. Battery Numbering was applied to either the Top or Bottom.