Seacoast defense in the United States
Seacoast defense was a major concern for the United States from its independence until World War II. Before airplanes, America's enemies could only reach her from the sea, making coastal forts an economical alternative to standing armies or a large navy. After the 1940s it was recognized that fixed fortifications were obsolete and ineffective against aircraft and missiles. However, in prior eras foreign fleets were a realistic threat, and substantial fortifications were built at key locations, especially protecting major harbors.
The defenses heavily depended on fortifications but also included minefields, nets and booms, ships, and airplanes. Therefore, all of the armed forces participated in seacoast defense, but the US Army Corps of Engineers played the central role in constructing fixed defenses.
Designs evolved and became obsolete with changes in the technology available to both the attacking forces and the defenders. The evolution of the US seacoast defense system is generally identified among several "systems", which are somewhat defined by the styles used, but more so by the events or trends which periodically stimulated new funding and construction.
- 1 Early defenses
- 2 Civil War
- 3 Post Civil War to the Creation of the Coast Artillery Corps
- 4 Taft Board and creation of the Coast Artillery Corps
- 5 World War I
- 6 Between World War I and World War II
- 7 World War II
- 8 Post war defensive missiles
- 9 See also
- 10 Notes
- 11 References
- 12 External links
At the beginning of the American Revolution many coastal fortifications already protected the Atlantic coast. Prior to independence from Britain, local communities or colonies bore the cost and responsibility for their own protection. Urgency would wax and wane based on the political climate in Europe. Most defenses were artillery protected by earthworks, as protection from pirate raids and foreign incursions. Though seldom used, the forts were a deterrent. Additional forts were built during the Revolution; usually built to meet specific threats.
When the United States gained independence in 1783, the seacoast defense fortifications were in poor condition. Concerned by the outbreak of war in Europe in 1793, the Congress created a combined unit of "Artillerists and Engineers" in 1794, appointed a committee to study coast defense needs, and appropriated money to construct a number of fortifications that would become known as the First System.
Twenty-one locations were selected to be fortified, mostly with traditional low walled structures with low sloped earthworks protecting wood or brick walls. The conventional wisdom was that soft earth would cushion the effect of cannon fire against the walls, and that low walls presented less exposure to projectiles. Walls were laid out at angles to each other forming a system of bastions, resembling a star layout, so that enemy forces could not mass against the bottom of a wall beneath the vertical field of fire from the wall; defenders on any wall could see and fire-on the base of the adjacent walls. The angled walls also reduced the chance for more destructive straight-on hits from cannonballs.
Lacking trained engineers to supervise the work, Secretary of War Henry Knox placed a number of European engineers under contract. Although some fine forts were constructed, for the most part enthusiasm and funding waned and little work was completed. Most of the partially finished earthworks and wooden structures deteriorated before they were needed to defend against the British in 1812.
In 1802 Congress separated the artillerists and engineers into separate corps and directed the Corps of Engineers to create a military academy at West Point, New York. One of the driving forces for establishing the new academy was the need to divorce the United States from its reliance on foreign engineers. In 1807-1808 new concerns over a possible war with Great Britain, prompted President Thomas Jefferson to renew fortification programs; this has come to be known as the Second System.
One common weakness among the typical low-walled open bastion or star forts was exposure to enemy fire, especially to new devices designed to explode in mid air and rain shrapnel down on the gunners. Gun emplacements which were at an angle to the sea were vulnerable to a solid shot running parallel to the wall taking out a row of guns and gunners with one enfilading shot. In the late 1770s a French engineer, the Marquis de Montalembert, advocated a major change in the design of fortresses to address these problems. His design protected a fort's gunners by placing most of them in covered casemate walls with openings for the guns. By stacking rows of casemates in high walls more guns could be mounted along shorter walls. This was particularly important for seacoast fortifications, which had only a limited time in which to fire at passing enemy ships. To build these tall forts, walls had to be built of masonry, but be very thick in order to withstand the pounding of cannon fire.
The Second System was distinguished from the First System by greater use of Montalembert's concepts and the replacement of foreign engineers by American ones, many of them recent graduates of the new United States Military Academy superintended by Major Jonathan Williams, who not only instructed the new engineers in new ideas of coastal defense, but also designed and constructed a prototype, Castle Williams on Governor's Island in New York Harbor.
Again, several fine forts were produced, but generally projects went unfinished, and between the First System and Second System little was prepared to resist the British in the coming War of 1812. However, no First System or Second System fortress was captured by the British. The invasion of Baltimore was prevented by Fort McHenry (along with its protecting shoreline batteries of Forts Babcock and Covington to the west, Fort Look-Out (or the Six-Gun Battery) on the peninsula to the rear in the west, a temporary naval battery across the Patapsco channel to the east at Lazaretto Point, and the sunken ships blocking both channels on either side of McHenry along with 20,000 militia dug in on the east side of the town at "Loudenschlager's Hill" - later "Hampstead Hill" in today's Patterson Park). In some cases even incomplete forts (some with fake wooden cannon barrels painted black pointed out the embrasures) were sufficient to deter attack from the sea. But, undefended and unfortified, Washington, D.C., the national capital, was burned after the land militia forces were routed at the Battle of Bladensburg northeast of the capital in Prince George's County, Maryland. Washington had one fort, Fort Warburton on the Potomac River just below Alexandria, Virginia, whose commander ordered the magazine blown when the passing British fleet appeared nearby, after the British had already occupied Washington. The present Fort Washington was built on the site of Fort Warburton in the early 1820s as part of the Third System. Among the many important and historic documents lost in the British burning of the Library of Congress were the plans to Fort Warburton and other Second System forts.
In 1816, following the War of 1812, Congress appropriated over $800,000 for an ambitious seacoast defensive system which was known as the Third System. A Board of Engineers for Fortifications, appointed by President James Madison, visited potential sites and prepared plans for the new forts. The Board's original 1821 report established the policy which would remain in place for most of the 19th century. The original report suggested 50 sites, but by 1850 the board had identified nearly 200 sites for fortification. The Army built forts at 42 of these sites, with several additional sites containing towers or batteries.
The forts were originally intended to mount mostly 42-pounder (7 inch or 178 mm) seacoast guns; however, due to a shortage of these weapons many 32-pounder (6.4 inch or 163 mm) seacoast guns and 8-inch (203 mm) and 10-inch (254 mm) Columbiads were mounted instead.
The main defensive works were often large structures, based on combining the Montalembert concept, with many guns concentrated in tall, thick masonry walls, and the Vauban concept, with layers of low, protected-masonry walls. Construction was generally overseen by officers of the Army's Corps of Engineers. Smaller works guarded less significant harbors.
By the end of the Third System in 1867, 42 forts covered the major harbors along the coastline. While most of the forts were completed, several of the forts - mostly in New England - were still under construction. A few of these forts, such as Fort Preble, Fort Totten, and Fort Constitution, were readied for armament even though they were far from complete.
The Corps of Engineers listed the forts from Northeast to Southwest, then to the Pacific Coast. The same order is used here for the new-construction forts of the Third System:
- Penobscot River, Maine: Fort Knox;
- Popham Bay, Maine: Fort Popham;
- Portland Harbor, Maine: Fort Gorges, Fort Scammell, Fort Preble;
- Portsmouth, New Hampshire: Fort McClary, Fort Constitution;
- Boston Harbor, Massachusetts: Fort Warren, Fort Independence;
- New Bedford, Massachusetts: Fort at Clark's Point (later Fort Rodman);
- Newport, Rhode Island: Fort Adams;
- New London, Connecticut: Fort Trumbull;
- New York City, New York: Fort Schuyler, Fort Totten, Fort Tompkins, Fort Richmond, Fort Hamilton, Fort on Sandy Hook, New Jersey (later Fort Hancock);
- Baltimore Harbor, Maryland: Fort Carroll;
- Washington, District of Columbia: Fort Washington;
- Norfolk, Virginia: Fort Monroe, Fort Calhoun (later Fort Wool);
- Beaufort, North Carolina: Fort Macon;
- Wilmington, North Carolina: Fort Caswell;
- Charleston, South Carolina: Fort Sumter;
- Savannah, Georgia: Fort Pulaski;
- St. Marys River, Florida: Fort Clinch;
- Key West, Florida: Fort Taylor;
- Dry Tortugas, Florida: Fort Jefferson;
- Pensacola Bay, Florida: Fort Pickens, Fort Barrancas, Advanced Redoubt, Fort McRee;
- Mobile Bay, Alabama: Fort Morgan, Fort Gaines;
- New Orleans, Louisiana: Fort Massachusetts, Fort Pike, Fort Wood (later Fort Macomb), Fort Jackson, Fort Livingston;
- San Francisco Bay: Fort Point, Fort Alcatraz.
In addition, several towers and batteries were constructed in support of the forts or at lesser harbors. First and Second System forts were renovated during the system as well, and readied for the larger cannon prevalent during that period. 
Again changes in technology affected design; the higher velocity ordnance of new rifled cannons crushed and penetrated the masonry walls of Third System forts. Severe damage was inflicted to forts on the Atlantic Coast during the Civil War. For example, Fort Sumter in South Carolina was bombarded into surrender by Confederate batteries in 1861, and reduced to rubble during Union efforts towards its recapture. In 1862 Fort Pulaski in Georgia was forced to surrender after only 30 hours of bombardment with rifled cannon, primarily large-caliber Parrott rifles.
Many of the larger smoothbore cannon (32-pounder and up) were rifled and equipped with breech bands to support larger powder charges and extend their effective range during the Civil War. This process is referred to as "banded and rifled".
The urgencies of war required that new forts or improvements be constructed quickly and at low cost. Partially completed Third System forts were finished, but new construction was mostly wood-revetted earthworks. Frequently earthworks were built near a Third System fort in order to supplement its firepower, but often they were stand-alone fortifications. In some cases cannon from masonry forts were dispersed to earthen bunkers where they were better protected. The fortification of San Francisco Bay is a good example, where the typical Third System Fort Point at the mouth of the bay was effectively replaced by dispersed earthworks and low-walled fortifications nearby on Alcatraz Island, Angel Island, the Marin Headlands, and Fort Mason.
During the Civil War underwater mines, at the time called a torpedo, became an important supplementary defense measure. The Confederacy, without a large navy to protect its harbors, relied on mines extensively to deter attacks by Union ships.
Coast Artillery Weapons During the Civil War
Numerous types of seacoast artillery were used in the Civil War. The following list includes only widely deployed weapons. See Siege artillery in the American Civil War for more information.
- Smoothbore weapons:
- 32-pounder (6.4 inch or 163 mm) and 42-pounder (7 inch or 178 mm) seacoast guns
- 8-inch (203 mm) and 10-inch (254 mm) Columbiads
- 8-inch, 10-inch, 15-inch (381 mm) and 20-inch Rodman guns
- Rifled weapons:
- Rifled and banded variants of 8-inch, 10-inch, and other smoothbore guns
- 6.4-inch (100-pdr), 8-inch (200-pdr), and 10-inch (300-pdr) Parrott rifles
- 6.4-inch and 7-inch (178 mm) Brooke rifles (Confederate made)
Post Civil War to the Creation of the Coast Artillery Corps
After the war, construction for several new Third System forts began in New England. These were to be built of stone rather than brick, and designed to accommodate the large-bore cannon developed during the war. However, in 1867 money for masonry fortifications was cut off, and the Third System came to a close.
The vulnerability of masonry to rifled cannon and large-caliber smoothbore cannon and fewer concerns for invasion led to the construction of well-dispersed masonry-revetted earthen fortifications with brick-lined magazines, often located near Third System forts. These were typically armed with 15-inch Rodman guns and 8-inch converted rifles; in some cases the forts were also rearmed with these weapons. All of the larger Parrott rifles had burst frequently during the war, so few of these were retained in service after the war. Also during the 1870s, a number of new projects were started to include large caliber mortars and submarine mines. However, the facilities for the mortars and mines were never completed. By the 1880s most of the earthen fortifications were in disrepair.
Monitors for Coast Defense
Though coastal defense was generally within the purview of the Army, the Navy became more involved in the late 19th century with coastal defense ships, generally called monitors. These monitors were turreted ironclad warships inspired by USS Monitor; as well as coastal ships which closely followed her design, the term 'monitor' also encompassed more flexible breastwork monitors which had a modest armored superstructure and were thus more seaworthy. These also featured modern rifled breech-loading guns.
Monitor-style ships were used extensively in offensive roles during the Civil War, but were impractical for ocean service and offensive action abroad. They were, however, ideally suited for harbor defense with their shallow draft and large guns. Postwar, Civil War-era monitors were dispersed to important harbors, including San Francisco on the west coast. From the 1870s to the 1890s larger and more powerful breastwork monitors were produced, such as the Amphitrite class, while the ocean-going navy was slow to make the transition to steel hulls and armor plating. An improvement on the monitors were coastal battleships such as the Indiana class of the 1890s.
As a result of the Spanish-American War and the acquisition of Hawaii and the Philippines, by 1900 the Navy was committed to ocean-going battleships, and ceased building monitors; however, some of the vessels remained in service up to World War I in combat-prepared roles, and as training or auxiliary vessels thereafter.
Coast Artillery Weapons Between the Civil War and Endicott Period
The Endicott Program was largely implemented 1895-1905. As Endicott facilities were constructed in each harbor defense area, the previous coastal defenses were usually abandoned. Only widely deployed weapons are listed. The larger Parrott rifles had shown a tendency to burst during the war, so few were retained in service after the war.
- 10-inch (254 mm) and 15-inch (381 mm) Rodman smoothbore guns
- 8-inch (203 mm) Rodman converted rifles (converted from 10-inch Rodman guns)
In 1885 US President Grover Cleveland appointed a joint Army, Navy, and civilian board, headed by Secretary of War William Crowninshield Endicott, known as the Board of Fortifications. The findings of the board illustrated a grim picture of existing defenses in its 1886 report and recommended a massive $127 million construction program of breech-loading cannons, mortars, floating batteries, and submarine mines for some 29 locations on the US coastline. Most of the Board's recommendations were adopted.
Prior efforts at harbor defense construction had ceased in the 1870s. Since that time the design and construction of heavy ordnance in Europe had advanced rapidly, including the development of superior breech-loading and longer-ranged cannon, making the US harbor defenses obsolete. In 1883, the Navy had begun a new construction program with an emphasis on offensive rather than defensive warships. These factors combined to create a need for improved coastal defense systems.
The Endicott Board's recommendations led to a large scale modernization program of harbor and coastal defenses in the United States, especially the construction of modern reinforced concrete fortifications and the installation of large caliber breech-loading artillery and mortar batteries. Typically, Endicott period projects were not fortresses, but a system of well-dispersed emplacements with a few large guns in each location. The structures were usually open-topped concrete walls protected by sloped earthworks. Many of these featured disappearing guns, which sat protected behind the walls, but could be raised to fire. Controlled mine fields were a critical component of the defense, and smaller guns were also employed to protect the mine fields from minesweeping vessels. Most of the Endicott fortifications were constructed 1895-1905.
Robert Fulton used the term "torpedo" to describe an underwater explosive device in 1805. Samuel Colt experimented with electrical firing of the torpedo. Electrically fired torpedoes, later termed mines, controlled from mine casemates ashore were associated with coastal fortifications.
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 as follows:
"I call your attention to the recommendation of the Secretary and the board that authority be given to construct two more cruisers of smaller dimensions and one fleet dispatch vessel, and that appropriations be made for high-power rifled cannon for the torpedo service and for other harbor defenses."
Army leaders realized that heavy fixed artillery required different training programs and tactics than mobile field artillery. With the Endicott Program well underway, the Artillery Corps was divided into two types: field artillery and coast artillery. This process began in February 1901 with the authorization of 30 numbered companies of field artillery (commonly called batteries) and 126 numbered companies of coast artillery. 82 existing heavy batteries were designated coast artillery companies, and 44 new CA companies were created by splitting existing units and filling their ranks with recruits. The head of the Artillery Corps became the Chief of Artillery in the rank of brigadier general with jurisdiction over both types of artillery.
The coast artillery became responsible for the installation and operation of the controlled mine fields that were planted to be under observation, remotely detonated electrically and protected by fixed guns. With that responsibility the corps began to acquire the vessels required to plant and maintain the mine fields and cables connecting the mines to the mine casemate ashore organized as a "Submarine Mine Battery" within the harbor defense command. The larger vessels, Mine Planters, were civilian crewed until the creation of the U.S. Army Mine Planter Service (AMPS) and Warrant Officer Corps to provide officers and engineers for the ships designated as Mine Planters in 1918. The mine component was considered to be among the principal armament of coastal defense works.
By the end of the Second World War such fixed coastal defenses were obsolete and the artillery branches were merged in 1950, with some of the Mine Planter vessels being transferred to the Navy and designated Auxiliary Minelayer (ACM / MMA).
Coast Artillery Weapons of the Endicott Period
These weapons were emplaced around 1895-1905. Only widely deployed weapons are listed. Most except the mortars, 3-inch guns, and some 6-inch guns were on disappearing carriages, with barbette carriages used for the remainder. Although some harbor defenses in less threatened locations were abandoned in the World War I era, many of these weapons remained in service until superseded by 16-inch guns and scrapped during World War II.
- 12-inch gun M1888, M1895, M1900 (305 mm)
- 12-inch mortar M1886, M1890 (305 mm)
- 10-inch gun M1888, M1895, M1900 (254 mm)
- 8-inch gun M1888 (203 mm)
- 6-inch gun M1897, M1900, M1903 (152 mm)
- 3-inch gun M1898, M1902, M1903 (76 mm)
Taft Board and creation of the Coast Artillery Corps
In 1905, after the experiences of the Spanish-American War, President Theodore Roosevelt appointed a new fortifications board, under Secretary of War William Howard Taft. They updated some standards and reviewed the progress on 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. 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. A new 14-inch gun was introduced in a few locations and improved models of other weapons were also introduced. 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 Field Artillery and Coast Artillery into separate branches, creating a separate Coast Artillery Corps (CAC), and authorized an increase in the Coast Artillery Corps to 170 numbered companies. In 1907 the 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.
One of the most extreme fortresses of the early 20th century was Fort Drum in Manila Bay of the Philippines. Originally a barren rock island, it was leveled by U.S. Army engineers between 1910 and 1914 and then built up with thick layers of steel-reinforced concrete into a massive structure roughly resembling a concrete battleship. The fort was topped with a pair of armored steel gun turrets, each mounting two 14-inch (356 mm) guns. Searchlights, anti-aircraft batteries, and a fire direction tower were also mounted on its upper surface. The 25-to-36-foot-thick (7.6 to 11.0 m) fortress walls protected extensive ammunition magazines, machine spaces, and living quarters for the 200 man garrison. The extensive level of fortification was not typical of the period, but driven by the exposed location. Although the design predated concerns about defense from air attack, the design proved to be exemplary for that purpose.
After the outbreak of war in the Pacific on December 7, 1941, Fort Drum withstood heavy Japanese air and land bombardment as it supported U.S. and Filipino defenders on Bataan and Corregidor until the very end. The fortress was among the last US posts to hold out against the Japanese and did not surrender until ordered by superiors after Corregidor had been overrun, but not until the US soldiers had sabotaged the guns and ordnance to prevent use by the Japanese. Ironically, even without the guns, the Japanese in Fort Drum were among the last holdouts when US forces recaptured the Philippines in 1945.
Mines as we know them today were frequently referred to as torpedoes in the 19th and early 20th centuries. The self-propelled torpedo as we know it was derived from the concept of the mine, with early submarines and torpedo boats evolving as defensive weapons in the 1890s to deliver torpedoes against attacking fleets. During early development, it was not clear whether submarines and torpedo boats would be in the purview of the Army or the Navy, since the Army was responsible for the use and development of stationary minefields and other fixed coastal defenses. As the range and potential uses of submarines and torpedo boats grew, it became more apparent that these were naval vessels, and both surface- and submarine-delivered torpedoes were an important aspect of naval coastal defense strategies. However, self-propelled torpedoes were not included in the US Army's coastal defenses. Shore launched Whitehead compressed air driven torpedos were the first deployed.
World War I
Submarines and airplanes became more important, with the former being a perceived if not actual threat to US harbors. This concern caused an increase in the use of mines and nets, and demand for superior artillery. However, as the war progressed it became more clear that the enemies did not have the resources to bring the war across the Atlantic, and progress diminished along with concerns. Curiously, despite the rise of air power in World War I, it received little consideration in US coast defense design until the late 1930s, probably due to the emergence of Japanese aircraft carriers as a threat.
A large-scale program to mount 12-inch mortars along with 8-inch, 10-inch, and 12-inch guns and some other weapons as railway artillery was partially implemented during and shortly after World War I, with the weapons withdrawn from less-threatened forts and from spares. A general program to reduce mortars from four per pit to two per pit created a surplus of these weapons. Despite a large-scale effort, of all these weapons only three 8-inch guns were delivered to France before the Armistice, due to shipping priorities. The mortars and 8-inch guns were on trainable mounts, thus were suitable for use as coast defense weapons; the other weapons were returned to the forts after the war. Sources indicated that up to 96 12-inch mortars and 47 8-inch guns were retained as railway coast defense weapons through World War II, with most of the 8-inch guns deployed and almost all of the mortars held in reserve. The US Navy implemented a more successful program that delivered five 14"/50 caliber railway guns to France in time to support the final Allied offensives. However, these weapons' mountings were not suitable for coast defense.
Coast Artillery Weapons of the Taft Period and World War I
A new 14-inch (356 mm) gun and improved versions of some Endicott period weapons were introduced 1905-1918, supplementing rather than replacing the previous weapons. The 14-inch guns were emplaced in the new harbor defenses of Los Angeles, the Panama Canal, and Manila Bay in the Philippines. A one-off 16-inch gun M1895 (406 mm) was also deployed on a disappearing carriage on the Pacific side of the Panama Canal in 1914; this was the first 16-inch gun in US service.
- 14-inch gun M1907, M1910 (356 mm)
- 12-inch mortar M1908, M1912
- 6-inch gun M1905, M1908
Between World War I and World War II
Airplanes were a minor but increasingly important factor in World War I, and the threat prompted changes to coastal defenses in the 1920s and 1930s. Demonstrations in the 1920s by US General Billy Mitchell showed the vulnerability of warships to air attack; this illustrated the use of aircraft for seacoast defense against ships, but also the vulnerability of defenses against air power. In the isolationist US, bombers were seen as more of a defense against naval attack than a strategic offensive weapon. However, planes like the Boeing B-17, which evolved as defensive weapons, turned out to have excellent offensive capacity as well.
In 1922, 274 Coast Artillery companies were authorized and 188 were active. During the year 44 more companies were inactivated, but 14 new companies were created for the Philippine Scouts, and a 15th in 1923. The Philippine Scouts, units of mostly Filipino enlisted men and mostly US officers, manned many of the coast defenses in the Philippines. The General Staff reconfirmed a commitment to artillery and mines as the most practical and cost-effective methods for seacoast defense, as an alternative to a larger Navy or Air Corps. In 1924 the CAC adopted a regimental system, consolidating the companies into 16 harbor defense regiments and two of Philippine Scouts. The total companies authorized were 289, with 144 active. From 1930 to 1932 the army drafted new defense projects for each harbor. In 1931 it established a Harbor Defense Board to supervise the execution of these projects.
The rapid evolution of dreadnought battleships 1905-1920 showed the need for improved coast defenses, as most Endicott and Taft period weapons were on short-range mountings and were not large enough to reliably defeat battleship armor. Thirty-two existing 12-inch M1895 guns were mounted on new long-range M1917 barbette carriages, including two one-gun batteries in the Philippines. Other new weapons were deployed, but in limited quantities due to budget constraints. 14-inch M1920 railway guns were added to the harbor defenses of the Panama Canal and Los Angeles, two at each location. The future of US coast defense was foreshadowed with the adoption of 16-inch (406 mm) guns, initially the 16-inch howitzer M1920 (25 calibers long) and 16-inch gun M1919 (50 calibers long). Four howitzers were deployed at Fort Story, Virginia and seven guns were deployed at four locations near Boston, Long Island, NY, Queens, NY, and Pearl Harbor, Hawaii. In 1922 the Washington Naval Treaty caused the US Navy to cancel the South Dakota-class battleships and the Lexington-class battlecruisers, surplusing 16-inch/50 caliber Mark II and Mark III barrels. About 70 guns were completed before the treaty went into effect, and the Navy wished to retain most of them for use in future battleships. Initially only 20 guns were transferred to the Army, who built a new version of the M1919 mount for the naval guns. However, only ten of these guns were deployed until 1940, in Pearl Harbor, Panama, and San Francisco. They were known as the 16-inch Navy gun MkIIM1 and MkIIIM1 in Army service. The 16-inch guns, firing 2,340 lb (1,060 kg) projectiles up to 49,100 yd (44,900 m), were much more effective than any previous coast defense guns.
Another weapon sparsely deployed in the 1930s would become a bigger part of World War II coast defenses. 8-inch/45 caliber Mark VI naval guns from older battleships scrapped under the Washington Naval Treaty became available, but only six guns were deployed 1933-38, all in fixed mountings. Up to 32 guns were initially available from the secondary armament of USS New Jersey (BB-16), USS Kansas (BB-21), USS Minnesota (BB-22), and USS New Hampshire (BB-25), of the Virginia- and Connecticut-class battleships. They were known as the 8-inch Navy gun MkVIM3A2 in Army service, and a railway mounting was developed in 1941. The main armament of these ships, the 12"/45 caliber Mark 5 gun, was also made available to the Army, but these were never deployed by the US and at least some were sold to Brazil.
Protection against air attack was slow to evolve. Existing batteries were camouflaged, but if detected, they remained vulnerable to air attack. The first batteries of heavy guns constructed after WWI were, somewhat inexplicably, completely open except for camouflage, but mounted long-range weapons set back from the coast out of direct observation from the sea. However, from the late 1930s these batteries were mounted under thick concrete casemates covered with vegetation to make them virtually invisible from above and well protected against bombing. Significantly, the Washington Naval Treaty prohibited major improvements to defenses in the Pacific including the Philippines, so the two long-range batteries at Fort Mills on Corregidor were never casemated. Another result was that 12 240 mm howitzers being shipped to the Philippines were deployed in Hawaii instead. In anticipation of a conflict with Japan, most of the limited funds available between 1933 and 1938 were spent on the Pacific coast; especially as Japanese aircraft carriers were operational by then. In 1939 the threat of war in Europe prompted larger appropriations and the resumption of work along the Atlantic coast.
A new weapon adopted by the US during World War I introduced road and cross-country mobility to the Coast Artillery. The 155mm Gun M1918 (6.1 inch), closely derived from the French 155mm GPF (Grand Puissance Filloux, or high-powered gun designed by Filloux), could be towed behind heavy Holt tractors and deployed to provide some protection for areas not part of existing harbor defenses. Circular concrete platforms called "Panama mounts" were added to existing defenses to improve the utility of these weapons.
In anticipation of war, additional mines, searchlights, radar, and anti-aircraft guns were installed in 1940 and 1941. After the war began, the entire Western Defense Command was placed on high alert, but Japanese attacks, including two submarine attacks and an explosive balloon, caused only minor damage.
Submarine nets and underwater mines protected many harbor entrances. Radar and patrol planes could detect enemy vessels at long distances, and aircraft became the first line of defense against intruders.
Coast Artillery Weapons Between World War I and World War II
The majority of Endicott and Taft period weapons remained in service between the wars. U.S. coast artillery introduced between the wars included:
- 16-inch gun M1919 (406 mm)
- 16"/50 caliber Mark 2 gun (also Mark 3)
- 16-inch howitzer M1920
- 14-inch M1920 railway gun (356 mm)
- 12-inch Gun M1895 on long-range M1917 barbette carriage (305 mm)
- 12-inch coast defense mortar (various models) on railway mounting
- 8-inch M1888 gun on railway mounting (203 mm)
- 8-inch Mk VI M3A2 gun (initially on fixed mountings)
- 155mm Gun M1918, a tractor-drawn French-designed weapon built for the U.S. Army (6.1 inch)
World War II
The air attack on Pearl Harbor demonstrated the obsolescence of coastal artillery; however, perhaps in its absence surface raiders would have been bolder. Coastal defense emplacements in the Philippines (the only occasion since the Civil War on which US coast defenses were heavily engaged) and Singapore were locally effective; however, the Japanese simply attacked where there were no defenses and then enveloped the fortifications. Heavily fortified positions such as Japanese Rabaul and Fort Drum in the Philippines demonstrated tactical success amongst strategic failures.
The outbreak of war in Europe in September 1939 and the Fall of France in June 1940 greatly accelerated US defense planning and funding. About this time a severe lack of design coordination resulted in the Iowa-class battleships being unable to use the Mark 2 and Mark 3 16-inch guns, and a new gun design was required for them. With war on the horizon, the Navy released the approximately 50 remaining guns, and on 27 July 1940 the Army's Harbor Defense Board recommended the construction of 27 (eventually 38) 16-inch two-gun batteries to protect strategic points along the US coastline, to be casemated against air attack, as were almost all of the older batteries by this time
The 16-inch guns were only the top end of the World War II program, which eventually replaced almost all previous coast defense weapons with newer (or remounted) weapons. Generally, each harbor defense command was to have two or three 16-inch or 12-inch long-range batteries, plus 6-inch guns on new mountings with protected magazines, and 90 mm Anti Motor Torpedo Boat (AMTB) guns. In addition to the proposed 38 new 16-inch (406 mm) batteries with a range of 25 mi (40 km), eleven new 8-inch (203 mm) batteries with a range of 20 mi (32 km) and 87 new 6-inch (152 mm) batteries with a range of 9 mi (14 km) were projected. All of these batteries had two guns each with heavily protected magazines and plotting rooms and casemated guns (except the 6-inch guns had shielded mountings). Additionally, about 24 8-inch MkVIM3A2 railway guns were mounted. In most cases replacing existing harbor defenses, fortifications were planned for the harbor defenses of:
With CONUS and the Caribbean less threatened as the war progressed, about 21 16-inch gun batteries were completed 1941-44, but not all of these were armed. Similarly, three 12-inch long-range batteries, five 8-inch batteries (mostly in Alaska), and about 65 6-inch batteries were completed, but some were not armed. Some batteries on Oahu were completed with 14-inch turrets from the sunken USS Arizona (BB-39) and 8-inch turrets removed from USS Lexington (CV-2) and USS Saratoga (CV-3) rather than the designed guns. As the areas of combat became more distant from the US and as naval threats were essentially removed, defending harbors against ships became a low priority, and as the new coast defense batteries were completed, almost all of the older seacoast guns were scrapped to become new weapons. Many soldiers of the Coast Artillery were transferred to anti-aircraft or even infantry duties. When the war ended, it was soon decided that seacoast defense guns were no longer needed, and missiles would eventually fill the role. By 1947 most guns remaining in the seacoast defense were declared surplus, and the last weapons were removed in 1950 when the Coast Artillery was deactivated.
Besides the Coast Artillery, key islands in the Pacific theater were defended by US Marine defense battalions throughout the war. Their most famous engagement was the Battle of Wake Island in December 1941, in which heavy casualties were inflicted on a Japanese invasion force that eventually took the island. The 155 mm Long Tom artillery piece, an evolution of the 155 mm GPF concept, was used in island and harbor defense in the Pacific from 1943 by both the Marines and the Army. Seven Coast Artillery Groups (155 mm Gun) were activated in May-June 1944; three were deployed to Okinawa and the Philippines in 1945 while one was activated on Trinidad; the remainder never left CONUS.
Coast Artillery Weapons During World War II
U.S. coast artillery during World War II relied primarily on weapons purchased between the wars. Essentially all of the Endicott and Taft period weapons were scrapped by late 1944 as new batteries were completed. The systems included:
- 16-inch gun M1919 (406 mm)
- 16"/50 caliber Mark 2 gun (also Mark 3)
- 16-inch howitzer M1920
- 14-inch M1920 railway gun (356 mm)
- 12-inch Gun M1895 on long-range M1917 barbette carriage (305 mm)
- 12-inch coast defense mortar (various models) on railway mounting (almost all in reserve)
- 8-inch M1888 gun on railway mounting (203 mm)
- 8-inch Mk VI M3A2 gun (on railway and fixed mountings)
- 155mm Gun M1918, a tractor-drawn French-designed weapon built for the U.S. Army (6.1 inch)
- 155 mm Long Tom gun M1/M2
- 6-inch gun M1903 in a new shielded mounting
- 90 mm gun M1 on fixed and towed mounts
- 3-inch gun M1903
Post war defensive missiles
Early in the Cold War, the Soviet Union developed long-range bombers which could reach the United States, and soon after exploded their first atomic bomb. Among the most threatened targets were harbors and naval bases. The mission of the Nike missile program was to act as a "last-ditch" line of air defense for selected areas. The Nike system would have been used if the Air Force's interceptors failed. With some anti-ship capability (especially the later nuclear-capable weapons), these were the last fixed-fortification weapons employed in the United States.
Nike sites were built during the 1950s in "rings" around major urban and industrial areas and key Strategic Air Command bases. The number of sites constructed within varied upon many factors. Due to the short range of the original Nike missile, the Nike "Ajax", many bases were located close to the center of the areas they protected. Frequently, they were located within heavily populated areas. By 1960 the longer-range, nuclear-capable Nike Hercules was deployed, with the Air Force's BOMARC missile system following soon after.
The missiles were considered obsolete by the mid-1960s, and the installations were removed in the early 1970s.
- Ripley, Warren (1984). Artillery and Ammunition of the Civil War. Charleston: The Battery Press. p. 71.
- Wade, pp. 137-139
- Weaver II, John R., A Legacy in Brick and Stone: American Coastal Defense Forts of the Third System, 1816-1867, Pictorial Histories Publishing, 2001, ISBN 1-5751006-9-X
- Ripley, pp. 17-44, 71-86
- Ripley, pp. 109-136
- National Park Service, Torpedo Defense - COAST DEFENSE OF THE POTOMAC
- Chester A. Arthur, Second Annual Message to Congress
- Coast Artillery Organization - A Brief Overview, Bolling W. Smith & William C. Gaines
- Army Warrant Officer History
- Ft. Miles, Principal Armament - Mine Field
- Berhow, pp. 70-199
- US Army Railway Artillery in WWI
- Berhow, pp. 61, 224-225
- Berhow, p. 225
- Berhow, pp. 192-193
- Berhow, pp. 190-191
- Friedman, pp. 311-313
- Berhow, pp. 176-177
- Berhow, pp. 80-81, 249-251
- Berhow, pp. 224-228
- Kirchner, D.P., CDR USN and Lewis, E.R., Capt USAR (January 1968). "American Harbor Defenses: The Final Era". United States Naval Institute Proceedings.
- Berhow, pp. 224-228
- Berhow, pp. 224-228
- Stanton, pp. 449-450
- Berhow, Mark A., Ed. (2004). American Seacoast Defenses, A Reference Guide, Second Edition. CDSG Press. ISBN 0-9748167-0-1.
- Friedman, Norman (1985). U.S. Battleships: An Illustrated Design History. Annapolis, Maryland: United States Naval Institute. ISBN 978-0-87021-715-9.
- Lewis, Emanuel Raymond (1979). Seacoast Fortifications of the United States. Annapolis: Leeward Publications. ISBN 978-0-929521-11-4.
- McGovern, Terrance and Smith, Bolling, American Coastal Defences 1885-1950 (Fortress series, Book 44), Osprey Publishing 2006, ISBN 1-8417692-2-3
- Potter, E. B. and Nimitz, Chester W., Sea Power, A Naval History, Second Edition, Naval Institute Press 1981, ISBN 0-8702160-7-4
- Stanton, Shelby L. (1991). World War II Order of Battle. Galahad Books. ISBN 0-88365-775-9.
- Wade, Arthur P (2011). Artillerists and Engineers: The Beginnings of American Seacoast Fortifications 1794-1815. Mclean, Virginia: CDSG Press. ISBN 978-0-9748167-2-2.
- Harbor Defenses of San Francisco The California State Military Museum
- United States Seacoast Defense Construction 1781-1948: a Brief History at the Coastal Defense Study Group, Inc. website
- List of all US coastal forts and batteries at the Coastal Defense Study Group, Inc. website
- FortWiki, lists all CONUS and Canadian forts
- Coast Artillery Organization, A Brief Overview CDSG, Inc.
- Guarding the United States and Its Outposts by Stetson Conn, Rose C. Engelman, & Byron Fairchild, United States Army Center of Military History, 2000
- "Gun Train Guards Ends of Panama Canal -- Rolling Fort Crosses Isthmus in Two Hours" Popular Mechanics, December 1934 pp.844-845 excellent drawings in article on the 14-inch M1920 railway gun
- Fort Adams Fort Adams Trust website
- Coastal Defense US National Park Service
- Coastal Defense GlobalSecurity.org
- FortWiki gun type list
- Coast Defense Study Group
- Description of Seacoast Guns 8, 10, 12, 14, 16-inch
- TM 4-210 page at the CDSG