Hormuz Tensions Renew Focus on Naval Fuel Security

By

The renewed threat of disruption to the Strait of Hormuz is again reminding defence planners of the vulnerability of global energy logistics in major conflicts. Naval modernisation is increasingly tied not only to weapons and sensors but also to energy resilience. Modern fleets are studying how warships could operate with a wider range of fuels if supply chains are disrupted during a conflict.

Roughly a fifth of the world’s traded oil normally passes through the narrow waterway linking the Persian Gulf to global markets. Any sustained military confrontation involving Iran and Western forces risks temporarily restricting tanker traffic, sending shockwaves through energy markets and raising immediate operational questions for navies that rely heavily on marine diesel and other petroleum-based fuels.

Although global supply chains have generally proven resilient in recent decades, recent war scenarios in the Middle East highlight a strategic vulnerability that defence planners have discussed quietly for years. Modern naval operations remain deeply dependent on fossil fuels transported through a relatively small number of maritime chokepoints.

Guided-missile cruiser USS Cape St. George (CG 71) and aircraft carrier USS Abraham Lincoln (CVN 72) transit the Strait of Hormuz on May 11th, 2012. (Image: U.S. Navy Photo by Mass Communication Specialist 3rd Class Alex R. Forster)

For NATO and European defence planners, the implications extend far beyond the Gulf. A prolonged disruption of Middle Eastern oil exports would affect the ability of allied fleets to sustain operations in distant theatres, including the Baltic Sea, where naval presence has become strategically important since Russia invaded Ukraine. The situation is therefore renewing interest in an idea that until recently was largely associated with commercial shipping and climate policy: diversifying naval propulsion and fuel supply systems.

Expanding Operational Flexibility

Commercial shipping companies are already experimenting with alternative fuels such as methanol, ammonia, hydrogen-derived fuels and advanced synthetic fuels. These technologies are being driven primarily by environmental regulation and the decarbonisation of global shipping. Yet the same technologies could also serve a strategic purpose by reducing reliance on a single fuel supply chain.

For military planners, the issue is less about abandoning oil entirely and more about expanding operational flexibility. Naval vessels capable of operating on multiple fuel types could reduce vulnerability to supply disruptions during major conflicts. They could also allow fleets to draw fuel from regional industrial sources rather than relying exclusively on global oil logistics.

In Northern Europe, where renewable electricity and advanced industrial processes are expanding rapidly, alternative maritime fuels could eventually be produced domestically. Countries around the Baltic Sea are already developing large-scale projects related to green hydrogen, synthetic fuels and other energy carriers.

If those technologies mature, they could offer NATO navies an additional logistical option during crisis situations. Instead of relying exclusively on global oil shipments passing through geopolitical chokepoints, fleets operating in northern waters could potentially draw fuel from regional industrial production. For now, the concept remains largely theoretical for military applications. However, the technological groundwork is being laid in the commercial sector. As alternative fuel systems become more common in civilian shipping, the defence sector may eventually find it advantageous to adopt similar capabilities.

Search for Alternative Fuels

The issue has gained attention in NATO navies as maritime decarbonisation technologies developed in commercial shipping begin to mature. Several navies and defence industries are therefore examining combinations of traditional marine fuels and emerging alternatives such as synthetic fuels, biofuels, LNG, methanol and ammonia.

The US Navy: Drop-in fuels and the Great Green Fleet

The most visible experiment was conducted by the United States Navy in the early 2010s as part of the Great Green Fleet initiative. The programme demonstrated that naval vessels and aircraft could operate on biofuel blends compatible with existing engines.

During exercises and deployments, U.S. Navy ships and aircraft operated using fuel blends that combined conventional petroleum with advanced biofuels derived from sources such as algae and waste oils. The concept was deliberately designed around Drop-in Fuels, meaning fuels that could replace conventional fuel without modifying engines or logistics systems.

The logic was straightforward. If biofuels behave identically to traditional fuels, the Navy can switch between them depending on price and availability while maintaining operational readiness. Blended fuels used in demonstrations typically combine petroleum fuel and biofuel in roughly equal proportions. Although large-scale adoption has been limited by cost, the programme established an important precedent: naval propulsion systems can operate with alternative fuels without redesigning entire fleets.

European Navies and the Commercial Shipping Transition

Wärtsilä’s MethanolPac, used to process and condition methanol on board a methanol-fuelled vessel for the supply of energy. (Image: Wärtsilä)

European naval planners are closely monitoring developments in the civilian maritime sector. Much of the technological innovation is happening in commercial shipping, where decarbonisation regulations are forcing shipowners to adopt new fuels.

Several European engine manufacturers are developing dual-fuel enginescapable of operating on multiple fuel types. These systems allow vessels to switch between fuels depending on availability and infrastructure.

Key fuels currently under development include:

  • Marine diesel and marine gas oil (MGO), the current global standards for naval propulsion
  • LNG (liquefied natural gas), already used in some civilian shipping
  • Methanol, including e-methanol produced with renewable energy
  • Ammonia, a potential zero-carbon fuel
  • Advanced biofuels and synthetic fuels

One of the leading developers is the Finnish engine manufacturer Wärtsilä, which has reported more than one hundred orders for dual-fuel ship engines by 2025. Its methanol-capable engine portfolio includes several models designed to run on methanol as well as conventional fuels. These engines are marketed specifically as fuel-flexible platforms, allowing operators to transition gradually to new fuels without abandoning existing infrastructure.

Methanol is attractive because it can significantly reduce emissions and can be produced synthetically using renewable electricity and captured carbon. According to Wärtsilä, methanol engines can also meet strict maritime emissions standards when combined with modern exhaust treatment systems. Ammonia is another candidate. In 2023–2024, Wärtsilä and Norwegian partners began developing ammonia-fuelled maritime engines, and the first ammonia-powered offshore supply vessel conversion is scheduled to enter service later in the decade. The technology could reduce greenhouse-gas emissions by more than 70 per cent compared with conventional diesel engines.

Nordic and European Strategic Interest

Several European navies are evaluating how such technologies might translate into military applications.

  • Norway has strong incentives to explore alternative maritime fuels due to its leadership in green shipping and offshore energy technology.
  • Denmark, with its large merchant fleet and shipbuilding sector, has also studied alternative propulsion systems for maritime security operations.
  • Germany participates in NATO energy-security programmes focused on improving operational resilience and diversifying military energy supplies.
  • Finland and Sweden, in addition to dual-use engine production, both countries also have commercial and strategic interests in the production of alternative maritime (and aviation) fuels, including fuels derived from renewable electricity and biomass such as energy wood.

For the moment, most warships still rely on marine diesel and gas turbine fuel, partly because naval vessels must operate globally where alternative fuel infrastructure is limited. Safety considerations also play a role. Ammonia is toxic, and methanol is flammable, which complicates their use on combat vessels that must survive battle damage.

The commercial sector is likely to determine the pace of change. As merchant fleets adopt alternative fuels and port infrastructure expands, navies may gain access todual-fuel logistics networks that make operational experimentation feasible. The transition toward flexible maritime fuels has several strategic implications:

  • Operational Resilience
    Fleets can operate even if one fuel supply chain is disrupted.
  • Interoperability with Civilian Infrastructure
    Warships could refuel using the same fuels as commercial shipping.
  • Energy Diversification
    Synthetic fuels produced with renewable electricity could reduce reliance on imported oil.

For regions such as the Baltic Sea and the Arctic, where renewable electricity and maritime industry clusters are already strong, this could eventually produce a new industrial ecosystem linking naval procurement, shipping technology and energy infrastructure.

Naval planners are therefore watching developments in commercial ship propulsion closely. The first generation of multi-fuel engines is already entering service in merchant vessels. If the technology proves reliable, the next phase may see future warships designed with similar flexibility in mind.

Read More:
×