Sea lines of communication

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China's Critical Sea Lines of Communication. In 2004, over 80 percent of Chinese crude oil imports transited the Straits of Malacca, with less than 2 percent transiting the Straits of Lombok. Click to enlarge. See also: China's String of Pearls China's Critical Sea Lines of Communication.png
China's Critical Sea Lines of Communication. In 2004, over 80 percent of Chinese crude oil imports transited the Straits of Malacca, with less than 2 percent transiting the Straits of Lombok. Click to enlarge. See also: China's String of Pearls

Sea Lines of Communication (abbreviated as SLOC) is a term describing the primary maritime routes between ports, used for trade, logistics and naval forces. [1] It is generally used in reference to naval operations to ensure that SLOCs are open, or in times of war, to close them. The importance of SLOCs in geopolitics was described in Nicholas J. Spykman's America's Strategy in World Politics published in 1942.

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In the American Revolutionary War and the Napoleonic Wars, the SLOCs were, for the most part, in the control of the British Navy. When the British lost control of them during the Revolution, the result was the fall of Yorktown and its biggest army and, ultimately, the war. In the Napoleonic era, maintaining belligerence throughout, the British embargoed and blockaded any country associated with Napoleon, which created large economic hardships and dislocations that played a part in people of France becoming disenchanted with Napoleon.

In World War I and World War II, the British and Germans declared mutual blockade and the Kriegsmarine attempted to close the SLOCs from North America to the British Isles with the use of submarines. In each case the Allies succeeded in keeping the sea lanes open. The Germans in each case failed to defeat the British naval blockade of Germany. The United States Navy in World War II successfully closed the SLOCs to Japan, strangling the resource-poor island nation.

Had the Cold War turned hot, Europe would have required resupply and reinforcement from North America. The Soviet Navy could potentially threaten and contest Atlantic SLOCs to support ground offensives in Europe.

Economic Importance of Sea Lines of Communication

Around 70-90 percent of global trade in volume and 70 percent in value is dependent on maritime transport and therefore open Sea Lines of Communication. [2] Maritime transport is of crucial importance to firm interest, as it allows Transnational Corporations to diversify their supply chains, access larger markets and reduce production cost. [3] Because Sea Lines of Communication enable this international linkage and make it profitable, they are a key driver of overall economic growth and stability. [2] [4] [5] [6] [7] Shipping, making use of open SLOC, as a “blue industry” is therefore important to secure economic growth and national interest. [5] [8] [9]

Threats to Economic Effectiveness of Sea Lines of Communication

There prevail challenges to maritime trade along SLOC, for example piracy and maritime terrorism. These can negatively impact global economic stability. [10] [5] Therefore, warships are used to secure SLOC and facilitate trade and alleviate pressure on national economies. [4] [11]

Piracy in the Gulf of Aden

Piracy in the Gulf of Aden had a negative economic impact, because it directly affected shipping along one of the most important SLOC connecting Europe to Asia through the Suez Canal. [12] Piracy attacks reduced bilateral trade value between two countries. [13] As a consequence, the cost of Somali piracy activity between the years 2000 and 2016 is estimated to lie between $1 billion to $25 billion annually. [14] [15] [13] These costs are incurred due to a loss of cargo, shipping delays, costs of introducing better security systems and the costs of ransom. [15] Furthermore, shipping costs for firms increased because of higher insurance risk premia, higher wages to account for higher risk of the crew and because firms switched to alternative forms of transportation, e.g. airborne or landbased transport. [14] Shipping costs also increased because of elevated fuel consumption from increasing travelling speed when crossing risk regions and rerouting along longer routes. [14] [16] The direct cost of rerouting due to Somali piracy in the Gulf of Aden amounted to $12 billion in 2010. [16]

Grey Zone Activity of Houthis in the Red Sea

Houthi activity in the Red Sea between 2023 and 2024 disrupted one of the most significant SLOC globally, connecting the European and Asian markets. [2] [12] [17] [18] [19] Around 12-15 percent of global trade and 30 percent of global container trade pass through the Suez Canal and through the Red Sea annually. [20]

Firstly, Houthi activity in the Red Sea increased operational costs of shipping companies by 18 percent. [12] Most major shipping companies like MSC, BP, and Maersk suspended the route through the Red Sea and Suez Canal and decided to reroute ships via the Cape of Good Hope. The rerouting of 67 percent of traffic increased transit around the Cape of Good Hope Route (CGHR) and added 10 to 14 days per trip for ships. [18] This caused higher fuel consumption as the route is 4,500 nautical miles longer than the Suez Canal Route (SCR), [12] which increased fuel costs by around $1 million per trip for shipping companies. [18] Additionally, rerouting caused a disruption in timetables and port calls, congestion in harbors, and delays. [21] Longer routes also required higher expenses due to higher wages, more maintenance and repairs. [18] Lastly, insurance risk premia increased from 0.07 - 0.2 percent of the cargo value to up to 2 percent if the vessel wanted to enter the Red Sea. [12] Because vessels were at sea longer and companies were mostly operating at full capacity, trade volume decreased and freight rates increased by between 124 and 339 percent. [12]

Secondly, East African countries like Djibouti, Kenya, Tanzania and Sudan were negatively impacted by the trade disruptions via the SCR. They experienced a shortage in perishables and normal containerized goods as between 10 percent (Tanzania) and 34 percent (Sudan) of their foreign trade volume are transiting this route. [22]

Thirdly, the Red Sea Crisis caused disruptions in the financial sector. Increased operational costs of shipping companies reduced dividends and served as a negative signal to investors. Because of this, investors exited the stock market which made stock prices more volatile and disrupted overall financial market stability. [19]

Lastly, Egypt saw declining government revenue due to decreased traffic along the SCR. The Suez Canal Authority reported a loss in canal toll revenues ranging from $175 million to $350 million between December 2023 and January 2024. [12] At the same time, companies explored long-term rerouting along the CGHR which could potentially introduce new trading opportunities for African countries along that route. [22] Demand in bunkering services can create new business ventures and promote infrastructure investments. This could cause economic development in the long-run. [22] Alternatively, shipping companies have considered modal alternatives or alternative routes like the Northern Sea Route (NSR). [12] Nonetheless, there remain viability concerns of this route because of reliance on Russian ports and adverse ecological impacts. [23]

See also

References

  1. ↑ "Global commerce and sea lines of communication in the Indian Ocean: A Sri Lankan perspective". Daily FT . April 10, 2019. Retrieved September 23, 2020.
  2. 1 2 3 Lau, Yui-yip, Qiong Chen, Mark Ching-Pong Poo, Adolf K.Y. Ng, and Chung Chui Ying. “Maritime Transport Resilience: A Systematic Literature Review on the Current State of the Art, Research Agenda and Future Research Directions.” Ocean & Coastal Management 251 (May 1, 2024): 107086–86. https://doi.org/10.1016/j.ocecoaman.2024.107086.
  3. ↑ Öge, Sevil . “Overview of International Maritime Trade.” Şengün & Partners Hukuk Yayınları, August 23, 2024. https://sengunlaw.com/overview-of-international-maritime-trade/.
  4. 1 2 Björnehed, Emma. “What Is the Value of Naval Forces?–Ideas as a Strategic and Tactical Restriction.” Defence Studies 22, no. 1 (July 27, 2021): 1–15. https://doi.org/10.1080/14702436.2021.1931133.
  5. 1 2 3 Bueger, Christian, and Felix Mallin. “Blue Paradigms: Understanding the Intellectual Revolution in Global Ocean Politics.” International Affairs 99, no. 4 (July 3, 2023): 1719–39. https://doi.org/10.1093/ia/iiad124.
  6. ↑ Tsailas, Demetrios N. “Risks and Threats in the 21st Century Maritime Security.” Security Science Journal 6, no. 1 (May 7, 2025): 106–44. https://doi.org/10.37458/ssj.6.1.7.
  7. ↑ UK Chamber of Shipping. “The Value of Shipping 2025: Powering Global Trade & Delivering a More Prosperous Nation,” 2025.
  8. ↑ Ghadigaonkar, Arya. “National Interest- a Geopolitical Instrument for Strategic Leverage?” THE GEOSTRATA, May 10, 2025. https://www.thegeostrata.com/post/national-interest-a-geopolitical-instrument-for-strategic-leverage.
  9. ↑ Jouffray, Jean-Baptiste, Robert Blasiak, Albert V. Norström, Henrik Österblom, and Magnus Nyström. “The Blue Acceleration: The Trajectory of Human Expansion into the Ocean.” One Earth 2, no. 1 (January 2020): 43–54. https://doi.org/10.1016/j.oneear.2019.12.016.
  10. ↑ Bueger, Christian. “What Is Maritime Security?” Marine Policy 53, no. 1 (March 2015): 159–64. https://doi.org/10.1016/j.marpol.2014.12.005.
  11. ↑ NATO. “Counter-Piracy Operations (Archived).” NATO, May 19, 2022. https://www.nato.int/cps/en/natohq/topics_48815.htm.
  12. 1 2 3 4 5 6 7 8 Notteboom, Theo, Hercules Haralambides, and Kevin Cullinane. “The Red Sea Crisis: Ramifications for Vessel Operations, Shipping Networks, and Maritime Supply Chains.” Maritime Economics & Logistics 26, no. 1 (February 20, 2024). https://doi.org/10.1057/s41278-024-00287-z.
  13. 1 2 Robitaille, Marie-Claire. “Maritime Piracy and International Trade.” Defence and Peace Economics 31, no. 8 (June 17, 2019): 957–74. https://doi.org/10.1080/10242694.2019.1627511.
  14. 1 2 3 Burlando, Alfredo, Anca D. Cristea, and Logan M. Lee. “The Trade Consequences of Maritime Insecurity: Evidence from Somali Piracy.” Review of International Economics 23, no. 3 (May 28, 2015): 525–57. https://doi.org/10.1111/roie.12183.
  15. 1 2 Galgano, Francis A. “Hostis Humani Generis: Pirates and Global Maritime Commerce.” Research in Globalization 8 (June 1, 2024): 100188. https://doi.org/10.1016/j.resglo.2023.100188.
  16. 1 2 Sandkamp, Alexander, Vincent Stamer, and Shuyao Yang. “Where Has the Rum Gone? The Impact of Maritime Piracy on Trade and Transport.” Review of World Economics 158 (October 8, 2021). https://doi.org/10.1007/s10290-021-00442-1.
  17. ↑ Nandini, Syamsul Ma’arif, Syamsunasir, and Pujo Widodo. “The Red Sea Crisis: Implications of the Houthi Attack on Maritime Trade and Global Security.” International Journal of Humanities Education and Social Sciences 4, no. 1 (2024). https://doi.org/10.55227/ijhess.v4i1.1135.
  18. 1 2 3 4 Rai, Alka. “Turbulent Waters in the Red Sea: Understanding Maritime Shipping Business Impacts and Implications.” Journal of Transportation Security 18, no. 1 (September 12, 2025). https://doi.org/10.1007/s12198-025-00299-7.
  19. 1 2 Yudaruddin, Rizky, Dadang Lesmana, Yanzil Azizil Yudaruddin, Norliza Che Yahya, and Ayesha Anwar. “Disruptions in Global Trade Routes: Market Reactions to the US–Houthi Conflict in the Consumer Cyclical Sector.” International Journal of Development Issues 24, no. 3 (January 13, 2025). https://doi.org/10.1108/ijdi-09-2024-0244.
  20. ↑ Helwa, Racha, and Perrihan Al-Riffai. “A Lifeline under Threat: Why the Suez Canal’s Security Matters for the World.” Atlantic Council, March 20, 2025. https://www.atlanticcouncil.org/in-depth-research-reports/issue-brief/a-lifeline-under-threat-why-the-suez-canals-security-matters-for-the-world/.
  21. ↑ Rodriguez-Diaz, Emilio, J. I. Alcaide, and R. Garcia-Llave. “Challenges and Security Risks in the Red Sea: Impact of Houthi Attacks on Maritime Traffic.” Journal of Marine Science and Engineering 12, no. 11 (October 23, 2024): 1900. https://doi.org/10.3390/jmse12111900.
  22. 1 2 3 Bacrot, Céline, and Marc-Antoine Faure. “Red Sea Crisis and Implications for Trade Facilitation in Africa | UNCTAD.” unctad.org, April 17, 2024. https://unctad.org/news/red-sea-crisis-and-implications-trade-facilitation-africa.
  23. ↑ Zhu, Shengda, Xiaowen Fu, Adolf K.Y. Ng, Meifeng Luo, and Ying-En Ge. “The Environmental Costs and Economic Implications of Container Shipping on the Northern Sea Route.” Maritime Policy & Management 45, no. 4 (March 5, 2018): 456–77. https://doi.org/10.1080/03088839.2018.1443228.

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