British nuclear submarine crews are being trained to fight off incoming drones with high-pressure jets of water from fire hoses. According to The Sun, this basic firefighting equipment is the only onboard air defense available to the Royal Navy’s Vanguard-class submarines, each valued at £4 billion ($5.2 billion).

The vessels carry powerful Trident II ballistic missiles, yet their crews have no dedicated onboard weapons to counter aerial threats. Instead, sailors must learn to use fire hoses as a last line of defense against unmanned aircraft approaching the submarines.

The threat is particularly serious when the vessels surface or remain docked. At Scotland’s Clyde naval base, Vanguard-class submarines can spend months or even years in port, leaving them especially exposed to drone attacks. Fire hoses are typically positioned on deck as a precaution, allowing crews to respond when necessary.

The Sun reports that the improvised defense is primarily intended to counter short- and medium-range FPV drones. Longer-range unmanned aircraft, meanwhile, could be intercepted by fighter jets. The hoses are fitted with special nozzles designed to help sailors aim powerful streams of water at airborne targets.

A source familiar with the arrangements explained that, in a worst-case scenario, crew members would deploy the equipment and attempt to knock an approaching drone off course or bring it down entirely.

The Royal Navy maintains that security at its submarine bases involves considerably more than fire hoses. Military officials point to several layers of protection, including physical barriers, regular patrols, surveillance systems and dedicated counter-drone equipment.

The revelations come amid wider concerns about the operational condition of Britain’s nuclear submarine fleet. In June, The Telegraph reported that every British nuclear-powered submarine was out of service and undergoing maintenance.

The Royal Navy operates four Vanguard-class ballistic missile submarines built during the 1990s. Armed with Trident missiles, these vessels form the backbone of Britain’s nuclear deterrent and provide the country’s only nuclear weapons delivery capability.