The USS Helena, a fast-attack nuclear submarine, surfaced in Guantanamo Bay, Cuba, a day after Russian naval forces arrived in Havana to conduct drills with the island nation, a Russian ally.

In a statement posted on X, US Southern Command said, “The fast-attack submarine USS Helena is in Guantanamo Bay, Cuba as part of a routine port visit as it transits the U.S. Southern Command geographic area of responsibility while conducting its global maritime security and national defense mission.”

A U.S. Navy fast-attack submarine arrived in Cuba's Guantanamo Bay on Thursday, hard on the heels of a Russian flotilla's arrival in Havana 24 hours earlier.

The USS Helena, one of around two dozen Los Angeles-class nuclear-powered, conventionally armed boats, was making "a routine port visit...while conducting its global maritime security and national defense mission," the U.S. Southern Command (SOUTHCOM) said in a statement on social media.

A group of Russian Navy vessels arrived in Cuba on Wednesday, a show of force by Moscow amid increasing tensions between the U.S. and Russia.

The vessels – the Russian frigate Admiral Gorshkov, nuclear-powered submarine Kazan, a rescue tug, and an oil tanker – entered Havana harbor with ceremonial firing from the Gorshkov and an 18th century colonial fort. The vessels are on a five-day official visit to Cuba in a show of ties between Moscow and Havana, according to CNN.