Naval Fortresses: An Old Concept for a New Era?

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Naval Fortresses: An Old Concept for a New Era?

If US naval dominance wanes, fortresses may once again become a viable strategic defense.

Naval Fortresses: An Old Concept for a New Era?
Credit: REUTERS/Darrin Zammit Lupi

Naval fortresses were once a major feature of naval warfare. That era passed with the start of the Cold War, when coastal installations were eclipsed by a combination of nuclear weapons and U.S. naval hegemony.

Historically naval fortresses played a critical role in several wars, such as the Port Arthur fortress in the Japan-Russia War and the Singapore Fortress in the Malayan Campaign of the Second World War. With the development of nuclear weapons for tactical applications during the Cold War, fortresses became obsolete because of their vulnerability to nuclear warheads. The mature anti-ship missiles of the 1960s presented a reasonable alternative to coastal defense as mobile deployment increased survivability. Additionally, U.S. naval hegemony and power projection through a global military presence have slashed the strategic value of fortresses, especially in the face of new U.S. technology, such as the GBU-28 Bunker-Buster.

New Strategic and Technological Conditions

But after two decades of U.S. hegemony in the post-Cold War era, the evolving international situation may revive the strategic and tactic value of naval fortresses. Several rising sea powers (like China), and Washington’s recent reluctance on overseas intervention, could shift the strategic circumstances of maritime states. As Washington D.C. hesitates to maintain the status quo, new naval powers have wider space to exert their maritime muscle over other coastal states, as China has done in the East and South China Seas for instance. Although these new sea powers may build up considerable surface and submarine fleets, fortresses would pose a significant obstacle to them.

Most land-attack and anti-ship missiles equipped on modern warships and submarines are loaded with relatively small warheads of less than a ton to facilitate a precision strike. As for gunfire, the main medium caliber guns, between 76mm and 155mm for modern frigates and destroyers, can only project shells of less than 150kg. Without nuclear warheads, the main weapon systems of modern surface ships and submarines would be unlikely to destroy fortresses, and anti-fortress missions would rely on special air-delivered munitions, such as bunker-buster bombs, because normal air-to-surface bombs and missiles are unable to effectively destroy fortresses.

The main constraints for these new sea powers would be their limited number of aircraft carriers and a lack of overseas bases. The very few non-U.S. aircraft carriers with ski-jump decks restricts both the number of operational aircraft and their payload, so a new sea power would be unlikely to be in a position to spare the capacity to effectively attack a fortress while other operations, such as establishing and maintaining air superiority, require those aircraft. Without an adequate overseas base, a new sea power would be unable to use land-based aircraft to carry out anti-fortress missions. That would make neutralizing a fortress a tough challenge for an emerging sea power.

By contrast, fortresses,  applying modern defense technology, advance both offensive and defensive capabilities. With intelligence support from satellites, radar and maritime patrol aircraft or drones, long-range anti-ship missiles (assisted by howitzers and torpedoes) can constitute an anti-access/area-denial (A2/AD) zone with a radius of hundreds of kilometers, which would be able to cover most straits and semi-closed sea areas. In terms of protection, most active defense systems used against surface vessels, including “hard-kill” means such as surface-to-air-missiles, close-in weapon systems, and “soft-kill” electronic warfare systems could be used with fortresses. With more space on land, those weapon systems can be optimally positioned with regard to performance. And without weight limits, diverse means of passive protection such as layered and reactive armor could be applied to the surface of fortresses to attenuate the effects of hostile munitions.

The Role of Fortresses in National Defense

Strategically, a coastal state’s fortresses can relieve the strategic pressure on its fleet and other military units. Because a fortress would attract most of an adversarial sea power’s attention, the coastal state’s fleet and other mobile forces could be used for other missions, such as flanking an enemy’s expeditionary force. In other words, the balance of force between a coastal state and a new naval power would not merely be a comparison of their vessels and aircraft. Whether gunboat diplomacy, limited warfare, or a major invasion, a new naval power will face more operational constraints and strategic deterrence from a fortress.

In another advantage, as many coastal states are highly urbanized, fortresses could reduce civilian casualties because of their fixed location. Contrast this with mobile units that have to hide in urban areas, resulting in greater collateral damage. Finally, as an A2/AD range of hundreds of kilometers would be sufficient to blockade most straits and some semi-close sea areas, if the adversarial sea power’s sea lines of communication (SLOC) pass through the A2/AD zone, the coastal state would have significant economic leverage over its adversary. Financially, compared to building major surface warships or submarines, fortresses would be cheaper and more survivable than vessels because of their heavy protection and the elimination of worries about buoyancy or mobility.


Undeniably, there are several restrictions to the use of fortresses. First, they have little utility in low density conflicts such as non-lethal warfare or fights involving paramilitary forces. Second, as in the Cold War era, fortresses are still vulnerable to nuclear attack, and may be unable to deter a non-rational invader.

Yet with America’s absolute monopoly on sea power declining, modernized naval fortresses provide coastal states both a relatively independent option to maintain their sovereignty, and deterrence in the face of newly emerging sea powers. That could be useful in this era of growing uncertainty.

Shang-su Wu is a research fellow in the Military Studies Programme, a constitute unit of the S. Rajaratnam School of International Studies (RSIS), Nanyang Technological University, Singapore.