Coastal Defense


Ten-inch guns on disappearing mounts at Fort Casey, Washington state. Source: The Coast Defense Study Group


Cannons of the Valdivian Fort System in Niebla, Chile, an example of a coastal defense.

Defense of one’s own coasts against enemy seaborne assault. Throughout history, the offensive use of naval power against the shore has prompted the development of countermeasures. However, it should be stressed that it is not the “coast” that is being defended, but something specific on the coast, such as a harbor, a naval base, or an anchorage suitable for invasion shipping. Classical examples of “coastal defense” include the 213–211 b.c. defense of Syracuse harbor against the Roman fleet with Archimedean machines. Because oared warships were short-ranged amphibious assets, they were normally employed within a littoral context, where their crew, and particularly their fighting men, served on land or sea as required. Such craft were the ideal reinforcement for fixed shore defenses. The introduction of gunpowder artillery only emphasized this link; scarce guns were shifted from ships to fixed defenses on shore and back again for tactical reasons.

The general adoption of heavy, gun-armed sailing ships as the basic warship type changed the nature of coastal defense. These ships could only use their firepower against a limited number of coastal positions, essentially harbors and deepwater inlets. Consequently, it made sense to fortify these positions, to deny them to an enemy who might otherwise push home an attack on valuable shipping or towns. An invasion—hitherto a simple matter of finding a reasonable beach on which to put shallow-draft oared vessels—now required control of secure deepwater anchorages.

King Henry VIII of England was among the first to meet the new challenge. Fearing attacks by France or the Hapsburg Empire, he built artillery fortifications to guard key anchorages on his southern coast. For the next 250 years coastal defense developed in scale and firepower, but the basic requirements remained static. The defending forces needed firepower and defensive strength to defeat any force of ships that could be brought against them. Carrying out a successful coastal defense was a relatively simple task, given the navigational problems of employing large sailing ships close to the shore, where hydrographic information was imperfect and the wind was particularly fickle.

By the end of the seventeenth century, coastal defenses had become so effective that the only naval assets able to bombard ports were heavy mortars mounted in small bomb vessels. These were useful, but never deployed in adequate numbers to achieve any lasting impact. By the late eighteenth century, the French Montalembert system of multilevel casemate batteries had been widely adopted, providing massive firepower at key points, such as Brest, Toulon, Kronstadt, and Havana. The British built less powerful forts to resist small-scale attacks, confident that their coast was defended by a superior battle fleet.

Invasion remained perfectly feasible for those with a superior fleet, because 99 percent of most national coastlines were undefended. Away from the deepwater harbors and ports, local defenses were inadequate and relied on the early arrival of a superior force of troops to drive off the small number of men who could be lifted and landed from the sea. In essence, large-scale overseas invasions were so costly and risky that few were undertaken. Instead, coastal raids—local operations requiring speed and surprise—were used, unless the target was a small island, which could be isolated and overwhelmed. Even then, amphibious commanders would land away from the fixed defenses and use their troops to deal with the sea defenses. The British captured Havana in 1762 employing this form of warfare.

After the 1805 Battle of Trafalgar the British used their absolute sea control to step up the projection of power from the sea. At Copenhagen in 1807, Walcheren in 1809, and Washington in 1814, armies were landed to attack naval or political targets of strategic importance. France, Denmark, and the United States were quick to upgrade their coastal defenses. The introduction of steam power from 1820 enabled such operations to outflank fixed defenses built in the eighteenth century, rendering them obsolete. Shell-firing guns greatly enhanced the firepower of heavy ships once they could be brought close to shore, while rockets added a new and conveniently compact area bombardment system. They had famously been used with mortars in the British attack on Fort McHenry at Baltimore in September 1814, and they are remembered in the U.S. national anthem.

By the mid-1850s the ability of steam-powered ships with shell guns to steam past existing coastal defenses and either bombard them or, far worse, simply ignore them had been demonstrated in the Crimean War. Anglo-French forces repeatedly outflanked Russian fixed defenses, and when they invaded the Crimea the Russian commander was so frightened that the Allies would steam into Sevastopol harbor that he scuttled half his fleet to keep them out. These fears led the Russians to adopt a new device, the submarine mine, which was first used in 1848–1849 by German insurgents against the Danish fleet off Kiel.

The submarine mine was a direct response to the steamship and promised to nullify the latter’s advantage of mobility. However, early Russian mines were too small, and they did little more than break a few cups and burn some eyebrows. By late 1855 the Russian coastal defenses had been shown to be utterly incapable of resisting the sophisticated layered-assault tactics developed by the British, especially when they were spearheaded by armored floating batteries. Despite their powerful coastal defenses, Sweaborg and Kinburn were overwhelmed, and the mightiest coastal defenses of all, those in Kronstadt, seemed equally vulnerable. Old defenses, based on stone batteries armed with smoothbore cannon, no longer met the need. Russia, lacking the industry and engineering talent to meet the challenge, made peace. Detailed reporting of the Crimean War influenced the next generation of coastal defenses, notably in the United States, where publication of the Delafield Report in 1860 prompted renewed defense construction.

The U.S. Civil War made greater demands on coastal defenses than any previous conflict, for the Confederacy was exposed on over 3,000 miles of coast as well as on a vast inland river network. Early Union successes, notably at New Orleans, reflected the lessons of the 1850s, as the U.S. Navy used steam power and firepower to run past powerful Confederate works. Once the South developed an integrated system of coastal defense, such triumphs were no longer possible. A combination of heavy artillery, mines, fixed barriers, and ironclads easily defeated the best the Union fleet (led by monitors) could offer at Charleston. Only when overwhelming firepower was combined with a strong amphibious force could such works be taken, a point made by the second attack on Fort Fisher in 1865.

Although the early use of torpedoes, fixed on the bow of attacking craft, added a new dimension to local defense, it was clear to all observers that attackers could now dominate any fixed defenses. This new ascendancy of attack persuaded Britain and France to concentrate 1860s dockyard development in river bases: Britain at Chatham, rather than at Portsmouth, and France at Rochefort, rather than Cherbourg. To make Portsmouth secure, the British built a ring of land forts to protect the base from forces landed farther down the coast, while three massive sea forts covered the deepwater approaches. These costly works were considered essential to secure the dockyard, the foundation of British sea power, against a surprise attack.

After 1865 masonry works gave way to earthworks, while longer-range artillery could be hidden and controlled for indirect fire. These guns were integrated with more powerful mines, torpedo-armed light craft, and defensive armored warships into a more effective system. However, the sheer cost of such defenses restricted them to a mere handful of locations at the vital naval bases. Even so, bases remained vulnerable to overwhelming naval attack, as the French recognized during the Fashoda crisis of 1898. No economic system of coastal defense could prevent attack from the sea if the objective was worthwhile.

In 1915 an Anglo-French fleet attempted to pass up the Dardanelles in the face of outdated Turkish forts. When the Allies were defeated by a handful of mines and artillery, many concluded that coastal defense had reestablished the superiority it had achieved in the sailing ship era. This was misleading, as the operation had been badly organized, poorly led, and lacked suitable ammunition to engage the forts. However, World War I did provide an answer. Aircraft could now pass over fixed defenses, just as steamers had outflanked them; bombardment was still possible. By 1939 aircraft were carrying out key naval strategic tasks, bombing dockyards, and using precision strikes against specific targets. This forced the defenders to deploy increasing numbers of aircraft.

World War II also saw a resurgence of amphibious power. Tactical air superiority, improved gunnery control, integrated tactics, and experience all enabled the Allies to stage strategic landings on three continents. Because of the sheer numbers involved, these operations could not avoid defended landing sites and had to take on heavy fixed defenses. Fearing such operations, Hitler tried to fortify the entire coast of his empire, building the Atlantic Wall from the Arctic Circle to the Spanish coast. Despite this effort, which employed guns, mines, and local army units, the Allies forced their way ashore on D-Day, while smaller-scale Japanese coastal defenses were swept aside in the Pacific by sea-based American operations.

Postwar nuclear weapons suggested that ports and harbors were defenseless and that large naval formations could be annihilated by a single weapon. This certainly called into question old concepts of coastal defense, and most gun batteries were done away with. Instead, western fears were of minelaying and clandestine operations by Soviet Spetsnaz forces. Even so, an attack against Soviet naval assets remained a core western naval task. It would be conducted by the nuclear-armed U.S. Navy, from carriers or, later, from submarines. The USSR quickly developed new coastal defenses, ultimately recognizing the indefensibility of anything above ground or water. Moscow planned to protect its nuclear deterrent forces by placing them inside defended ballistic submarine bastion areas. Even these were not safe; the 1986 U.S. Navy “New Maritime Strategy” saw them as the focus for decisive battles, while the subsequent “From the Sea” and “Forward from the Sea” doctrine reemphasized the dominance of power projection. By the late 1990s tactical weapons fired from the sea could strike countries without coastlines, such as Afghanistan, let alone those with coastlines. While cheap surface-to-surface missiles are now widely available for coastal defense, their record in the past two decades has not been particularly impressive. Defense against the superior flexibility, lift, and self-sufficiency of sea-based forces remains as much of a problem now as it has ever been.


Clarke, George Sydenham. Fortification: Its Past Achievements and Future Progress. New York: Dutton, 1907.

Lewis, Emanuel Raymond. Seacoast Fortifications of the United States: An Introductory History. Washington, DC: Smithsonian Institution Press, 1970.

Perry, Milton F. Infernal Machines: The Story of Confederate Submarine and Mine Warfare. Baton Rouge: Louisiana State University Press, 1965.