Russia has doubled the number of trained dolphins defending its Black Sea fleet from Ukrainian attacks, says report

• Russia appears to have doubled the number of trained dolphins defending its Black Sea fleet.
• The dolphins at the naval base in Sevastopol are trained to detect Ukrainian special forces divers.
• Russia's dolphins have an "inherent advantage," as "no one can out-swim a dolphin," one expert reported.

Russian forces have doubled the number of trained dolphins defending its Black Sea fleet in the Crimean peninsula against Ukrainian attacks, according to analysis by Naval News.

The Russian Navy has previously used militarized dolphins to protect its naval base at the harbor of Sevastopol, Insider reported last year, as a means of preventing Ukrainian undersea operations from sabotaging Russian ships.

Satellite imagery at the time captured by Maxar Technologies shows two pens containing the trained dolphins.

The number of dolphins being kept at the port has recently doubled from three or four to six or seven, H I Sutton, an expert on submarine and sub-surface systems and technologies, wrote for Naval News this week.

This comes after several drone attacks targeting Russia's ships in the area, as Ukrainian forces launched their recent counteroffensive in the long-running conflict.

Sevastopol is a major port and headquarters of Russia's Black Sea fleet in Crimea. The Black Sea peninsula was invaded by Russian forces and illegally annexed by Putin in 2014.

The animals are trained to defend against Ukrainian special forces divers — or combat swimmers — who might try to invade the base.

The dolphins have an "inherent advantage," as "no one can out-swim a dolphin," Sutton reported. Dolphins can reach speeds of 37 mph.

Russia's military has operated a trained marine mammal program in Sevastopol since the Cold War, according to the US Naval Institute.

Marine animals in these programs, including dolphins and beluga whales, are trained to find combat swimmers and detect mines, according to Sutton.

"Our specialists developed new devices that convert dolphins' underwater sonar detection of targets into a signal to the operator's monitor," a source told Russian news agency RIA Novosti last year, per The Telegraph.

The US Navy has also trained marine animals for military service, as well as in Sweden and possibly Israel and North Korea, per the Naval Times.