The U.S. Army Coast Artillery Corps (CAC) was an administrative corps responsible for coastal, harbor, and anti-aircraft defense of the United States and its possessions between 1901 and 1950. The CAC also operated heavy and railway artillery during World War I.

History

As early as 1882 the need for heavy fixed artillery for seacoast defense was noted in Chester A. Arthur's Second Annual Message to Congress where he noted:

In 1885 the Endicott Board was convened under the subsequent Grover Cleveland administration, chaired by Secretary of War William Crowninshield Endicott. This board recommended a large-scale program of harbor defenses at 29 ports, including guns, mortars, and mine fields. Most of their recommendations were implemented and new defenses were constructed by the United States Army Corps of Engineers between 1895 and 1905. As the defenses were constructed, each harbor or river's installations were controlled by Artillery Districts, renamed Coast Defense Commands in 1913 and Harbor Defense Commands in 1925. With the 1913 renaming, Artillery Districts became regional commands, each including several coast defense commands.Fort and Battery list at the Coast Defense Study Group website

An extensive fire control system was developed and provided for the forts of each Artillery District.FM 4-15, Coast Artillery Field Manual - Seacoast Artillery Fire Control and Position Finding, U.S. War Department, 1940, Government Printing Office: Washington, DC.

1901 reorganization Army leaders realized that heavy fixed artillery required different training programs and tactics than mobile field artillery. Prior to 1901 each of the seven Regular Army artillery regiments contained both heavy and light artillery batteries. In February 1901 the Artillery Corps was divided into two types: field artillery and coast artillery. The previous seven artillery regiments were dissolved, and 30 numbered companies of field artillery (commonly called batteries) and 126 numbered companies of coast artillery (CA) were authorized. 82 existing heavy artillery batteries were designated as coast artillery companies, and 44 new CA companies were created by splitting existing units and filling their ranks with recruits. The company-based organization was for flexibility, as each harbor defense command was differently equipped and a task-based organization was needed. The Coast Artillery would alternate between small unit and regimental organization several times over its history. The head of the Artillery Corps became the Chief of Artillery in the rank of brigadier general with jurisdiction over both types of artillery.Coast Artillery Organization – A Brief Overview, Bolling W. Smith & William C. GainesBerhow, pp. 423-426

Controlled mine fields

the Coast Artillery took responsibility for the installation and operation of the controlled mine fields from the Corps of Engineers; these were planted to be under observation, remotely detonated electrically, and protected by fixed guns. With that responsibility the Coast Artillery began to acquire the vessels required to plant and maintain the minefields and cables connecting the mines to the mine casemate ashore organized as a "Submarine Mine Battery" within the installation command, "submarine" meaning "underwater" in this case. The larger vessels, called "mine planters", were civilian crewed until the creation of the U.S. Army Mine Planter Service (AMPS) and Warrant Officer Corps in 1918 to provide officers and engineers for the ships designated as mine planters.Army Warrant Officer History The mine component was considered to be among the principal armament of coastal defense works.

Taft Board and the creation of the Coast Artillery Corps In 1905, after the experiences of the Spanish–American War, President Theodore Roosevelt appointed a new board on fortifications, under Secretary of War William Howard Taft. They updated some standards and reviewed the progress of the Endicott board's program. Most of the changes recommended by this board were technical; such as adding more searchlights, electrification (lighting, communications, and projectile handling), and more sophisticated optical aiming techniques. The board also recommended fortifications in territories acquired from Spain: Cuba and the Philippines, as well as Hawaii and a few other sites. Defenses in Panama were authorized by the Spooner Act of 1902. Due to rapid development of the dreadnought battleship type, a new gun was introduced in a few locations, including Los Angeles, the Philippines, Hawaii, and Panama. The Japanese were acquiring capital ships with guns of this caliber, beginning with Kongō in 1913. The Taft program fortifications differed slightly in battery construction and had fewer numbers of guns at a given location than those of the Endicott program. By the beginning of World War I, the United States had a coastal defense system that was equal to any other nation.

The rapidity of technological advances and changing techniques increasingly separated coastal defenses (heavy) from field artillery (light). Officers were rarely qualified to command both, requiring specialization. As a result, in 1907, Congress split the Field Artillery and Coast Artillery into separate branches, creating a separate Coast Artillery Corps (CAC), and authorizing an increase in the Coast Artillery Corps to 170 numbered companies. National Guard coast artillery units were also formed by the states to attempt to bring the CAC up to strength in wartime. Confusingly, many of these units were designated Coast Artillery Corps of their respective state National Guards. In 1907 the United States Army Field Artillery School at Fort Monroe became the Coast Artillery School, which operated until 1946, and in 1908, the Chief of Artillery became the Chief of Coast Artillery in the rank of major general.

World War I

As with the rest of the US Armed Forces, the Coast Artillery was undermanned and poorly equipped except for coastal artillery weapons when war broke out in Europe in 1914. The War Department formed a Board of Review that recommended an increase in strength, which resulted in 105 new CA companies in 1916–17, although these were initially undermanned. After the American entry into World War I, the Coast Artillery as a whole was ordered brought up to strength, and 71 new companies were organized by July 1917.

In response to the rapid improvements in dreadnought battleships, approximately 14 two-gun batteries of 12-inch guns on a new M1917 long-range barbette carriage began construction in 1917, but none were completed until 1920.

The Coast Artillery was designated to provide the personnel for all US-manned heavy artillery (155 mm gun and larger), almost all railway artillery, and later anti-aircraft artillery units. As with most US Army World War I equipment, these units were primarily equipped with French- and British-made weapons, with few American-made heavy weapons arriving in France before the Armistice. As with other American World War I units, the CAC units operated alongside French forces for the most part. The CAC units sent to France and Britain with the American Expeditionary Forces (AEF) were organized into a total of 11 brigades comprising 33 regiments of 24 guns each, plus a replacement regiment, nine trench mortar battalions and thirteen anti-aircraft battalions (a.k.a. sectors). Many Coast Artillery companies were withdrawn from stateside coast defenses to provide cadre for the new artillery regiments.Rinaldi, pp. 150-168History of the Coast Artillery Corps in World War I at Rootsweb.com However, only 13 regiments saw action, while the remaining 20 regiments did not complete training before the Armistice, and up to 6 of these never received guns. A total of 61 regiments were organized; however, at least 23 of these were organized in the US shortly before the Armistice and were soon disbanded.Rinaldi, pp. 159-160 The coast defense commands retained a company-based organization. Only one regiment saw action equipped with US-made guns, the 58th Coast Artillery armed with the 8-inch howitzer M1917, based on the British BL 8-inch howitzer Mk VI.58th Artillery (CAC) at Rootsweb.com

Ninety-five 6-inch guns were withdrawn from coast defenses, with an additional 46 weapons supplied by the Navy and 30 ex-Navy weapons from arms dealer Francis Bannerman. Seventy-two of the Army 6-inch guns (possibly with a few additional Navy weapons) and 26 5-inch guns also removed from coast defenses were mounted on M1917 field carriages and equipped four artillery regiments in France, but none of these completed training before the Armistice.Williford, pp. 92-99 After the war, some of the 6-inch guns were returned to coast defenses, but the 5-inch guns were withdrawn from coast defense service. Most of the 6-inch guns were stored and were eventually deployed in World War II.

No US railway guns existed when the US entered World War I in early 1917. Due to low production and shipping priorities, the Army's railway gun contribution on the Western Front consisted of four CA regiments operating French-made weapons. These were organized as the 30th Separate Artillery Brigade (Railway), also designated as the Railway Artillery Reserve (RAR), which usually operated mingled with French units in an Allied RAR.Order designating the 30th Brigade as the Railway Arty Reserve, 3 April 1918 The 40th Artillery Brigade of three regiments was also a railway artillery brigade of the RAR; however, it did not complete training before the Armistice.

The US Navy manufactured and operated five 14"/50 caliber railway guns that were delivered in time to support the final Allied offensives. With a view to getting numerous US-made weapons into the fight eventually, the Army also converted some of the many US coast artillery weapons to railway mounts. A total of 96 8-inch guns, 129 10-inch guns, 49 12-inch guns, and 150 12-inch mortars could be taken from fixed coast defense batteries or spares. Twelve 7-inch ex-Navy guns and six 12-inch guns being built for Chile were also available.

None of the army weapons were shipped to France except three 8-inch guns and some 10-inch barrels (to be mounted in France), as few of any type were completed before the Armistice. Forty-seven 8-inch railway guns were ordered, with 18 completed by the Armistice and the remainder completed later. Eight 10-inch railway mounts of 54 ordered were completed by this time, and twelve 12-inch railway mounts were completed by 1 April 1919. Three railway mountings for the Chilean 12-inch guns were ready for shipment by the Armistice; the remaining three barrels were retained as spares. Ninety-one 12-inch railway mortars were ordered, with 45 complete by 7 April 1919 and all major components of the remainder also complete. It is unclear how many additional railway guns and mortars were completed, but all 47 8-inch weapons and probably the 91 12-inch mortars were.US Army Railway Guns in World War I The 7-inch and 8-inch guns and 12-inch mortars used a common carriage, with outriggers and a rotating mount allowing all-around fire. This allowed the weapons to be used in coast defense against moving targets.

The 8-inch guns and 12-inch mortars were retained on railway mountings after the war, while most of the 10-inch and 12-inch guns were returned to the coastal forts.Miller, H. W., LTC, USA Railway Artillery, Vols. I and II, 1921, Vol. I, pp. 131-155 The 7-inch railway guns most likely became fixed coast artillery, although some were eventually transferred to Brazil as railway guns in 1941.Williford, pp. 100-101

The official birthday of the Army Warrant Officer Corps is 9 July 1918, when an Act of Congress established the Army Mine Planter Service as part of the Coast Artillery Corps, replacing previous civilian manning of mine planter vessels. Implementation of the Act by the Army was published in War Department Bulletin 43, dated 22 July 1918.