For centuries, nations going to war usually tried to blockade, or “close off”, an enemy nation’s ocean ports, in order to damage their commerce, but usually to support a land attack to capture said ports. Sometimes, though, as with American Civil War, blockades would sometimes extend to every ocean port in an enemy nation. With the end of World War Two, however, the massive wars of the previous one hundred and fifty years, the idea of the naval blockade began to wane, with only those nations with vast naval establishments being able to enforce such strategies, usually in concert with all kinds of “soft” measures, such as economic and financial sanctions.
However, the ancient concept of naval blockade — one of the most basic strategies of maritime warfare — is experiencing a significant revival and transformation in the 21st century. While the fundamental purpose remains unchanged — denying an adversary access to maritime commerce and resources — both the methods of implementation and countermeasures have evolved dramatically, creating new strategic and legal challenges in an increasingly connected global economy.
Traditional blockades relied on the physical presence of warships creating a cordon around enemy ports. Today’s “modern blockade” operates across multiple domains simultaneously. The ongoing situation in the Red Sea demonstrates this evolution, with Houthi forces effectively creating a blockade-like effect despite possessing no significant naval forces. Using a combination of medium-weight helicopters, shore-based anti-ship missiles, unmanned explosive boats, and aerial drones, non-state actors can now threaten maritime traffic with capabilities previously limited to nation-states.
Modern Houthi attacks and Somali piracy operations share surprising tactical and strategic parallels with their Caribbean predecessors from the “Golden Age of Piracy” (1650-1730), despite the centuries and thousands of miles between them.
Like the Caribbean pirates who established bases in lawless territories such as Nassau and Tortuga, both Somali pirates and Houthi forces operate from ungoverned or weakly governed coastal regions. The Somalis launched out from the collapsed state’s coastline, while the Houthi rebels utilize Yemen’s western shores as launching points for maritime attacks.
The economic logic remains strikingly similar. Caribbean pirates targeted the Spanish treasure fleet system, focusing on predictable shipping lanes where valuable cargo was concentrated. Similarly, Somali pirates focused on the narrow Gulf of Aden transit, while Houthis target the Bab el-Mandeb Strait directly — both critical chokepoints where shipping is concentrated and vulnerable.
Where they differ significantly is in motivation. Caribbean pirates primarily sought economic gain, as did Somali pirates through their sophisticated ransom systems. Houthi attacks, while sometimes involving seizure of vessels, function primarily as political and strategic actions within a broader regional conflict framework, making them more akin to privateers — state-sanctioned maritime raiders — than purely profit-driven pirates, due to their open and acknowledged status as a proxy force of Iran.
This diffusion of anti-access capabilities has democratized blockade tactics. Advanced anti-ship cruise missiles with ranges exceeding 200 nautical miles allow even smaller nations to threaten shipping across vast areas without maintaining a substantial fleet. The Chinese DF-21D “carrier killer” missile and similar systems enable “blockade at a distance” strategies that would have been impossible in previous eras. Similarly, while older anti-ship missiles like the Chinese HY-2 “Silkworm” is no longer effective against modern warships, they are highly effective against civilian cargo vessels with no electronic counter-measures (ECM) defenses. More importantly, for non-state actors, these older weapons are cheap, and relatively available on the international arms black market.
Cyber operations represent perhaps the most revolutionary development in blockade evolution. Naval strategists now consider port management systems, shipping logistics networks, and maritime communication channels as critical vulnerability points. A coordinated cyber attack could potentially halt port operations more effectively than physical presence, causing ships to be redirected or delayed without firing a shot. In 2017, the NotPetya malware attack against global shipping giant Maersk and Ukraine demonstrated how digital disruption could cause billions in shipping losses without a single warship deployment.
The legal framework governing blockades has struggled to keep pace with these technological developments. The traditional requirements under international law—including formal declaration, effectiveness, and impartiality toward neutral shipping—become ambiguous when applied to over-the-horizon missile threats or cyber disruptions. This creates dangerous gray zones where actions may have blockade-like effects without triggering the legal thresholds that would permit countermeasures.
These developments have prompted significant changes in how major naval powers prepare for both implementing and countering blockades. The U.S. Navy has invested heavily in both offensive and defensive capabilities, developing distributed maritime operations concepts that could sustain blockade operations despite adversary counter-targeting. Similarly, China’s naval expansion focuses on both area-denial systems to prevent blockade of its own ports and blue-water capabilities that could potentially blockade Taiwan or other regional adversaries.
Commercial shipping has also adapted. Insurance markets now incorporate blockade-like threats into their risk models, with specialized “war risk” policies for vessels transiting threatened regions. Major shipping companies have developed sophisticated contingency routing options and increased their resilience through distributed logistics networks.
For smaller maritime nations, this evolution presents particular challenges. Without robust naval capabilities or alternative supply routes, these countries remain vulnerable to both traditional and next-generation blockade tactics. Regional security organizations have increasingly focused on developing collective maritime security arrangements specifically addressing these asymmetric maritime threats.
Naval mines remain among the most cost-effective maritime weapons, offering asymmetric capabilities with significant strategic impact. Modern mines have evolved far beyond the contact mines of previous wars into sophisticated “smart” systems with advanced sensors, targeting algorithms, and activation mechanisms.
Today’s mines feature acoustic, magnetic, pressure, and seismic sensors that can identify specific vessel signatures, allowing them to selectively target certain ship classes while ignoring others. Advanced mines can lie dormant for months or years, activate on a predetermined schedule, or respond to remote commands. Some incorporate anti-handling features specifically designed to counter minesweeping operations.
Air-dropped mines represent a particularly flexible deployment method, a method in use since World War 2. Aircraft like the B-52, P-8 Poseidon, and various fighter platforms can rapidly seed large areas without risking surface vessels. The US Quickstrike series of air-delivered mines can be deployed from standoff ranges, allowing mining operations even in contested waters. The addition of JDAM kits to create the Quickstrike-ER has extended deployment ranges to over 40 nautical miles.
Countering these threats, modern mine countermeasure operations increasingly rely on unmanned systems rather than traditional minesweepers with human crews. Unmanned surface vessels (USVs) and underwater vehicles (UUVs) equipped with synthetic aperture sonar and other detection technologies can locate and map minefields with minimal risk. Once detected, neutralization occurs via ROV-delivered charges or specialized mine-hunting drones.
Despite technological advances in countermeasures, the fundamental asymmetry remains: mines are inexpensive to deploy but expensive and time-consuming to clear, making them particularly effective for sea denial strategies by smaller naval powers or non-state actors.
Perhaps most concerning is how these evolutionary developments have made naval blockades more attractive as “gray zone” operations—actions that remain deliberately below the threshold of conventional warfare while achieving strategic effects. A nation or non-state actor could significantly disrupt an adversary’s economy through blockade-like actions while maintaining plausible deniability or legal ambiguity.
As maritime commerce remains the backbone of global trade, with approximately 90% of international goods traveling by sea, the evolution of blockade tactics represents a significant security challenge for the international order. Nations must now prepare for blockade scenarios ranging from traditional warship deployments to sophisticated multi-domain operations combining kinetic, electronic, and cyber elements — a substantial evolution from the wooden ships that once enforced the traditional “close blockade” of previous centuries.
ADDITIONAL RESOURCES
- Wayne P Hughes Jr. USN (Ret.) (2018), Fleet Tactics and Naval Operations, Third Edition
- Julian Thompson (1994), Lifeblood of War: Logistics in Armed Conflict
- Thomas Ricks (2012), The Generals
- James F. Dunnigan (2003), How To Make War, 4th Edition
- James F. Dunnigan (1991), Shooting Blanks
