The US Navy’s Los Angeles-class submarine USS Newport News is pictured above sailing into Gibraltar yesterday evening.
The Ministry of Defence said it was “a scheduled logistical visit”.
The submarine’s arrival was not without incident, however.
Details were sketchy as this edition went to press, but eyewitnesses said a Spanish customs boat was intercepted by a Gibraltar Defence Police vessel after it came too close to the US submarine.
Officials at the MoD and The Convent were looking into the incident last night to establish the sequence of events and assess what happened and where.
If classed as an incursion, the incident will almost certainly draw a diplomatic protest, as happens as a matter of routine with all incursions by Spanish state vessels.
This is the second US submarine to visit Gibraltar this year.
Last March, the Virginia-class submarine USS John Warner stopped in Gibraltar en route to the eastern Mediterranean, where it was later involved in a military strike on targets in Syria.
The submarine fired six Tomahawk missiles at chemical weapon sites in Syria.
The USS Newport News was last in Gibraltar in 2016, where it spent several days undergoing what the MoD described at the time as “un-planned, non-nuclear maintenance work”.
The submarine is one of a class of nuclear-powered fast attack submarines that forms the backbone of the US Navy’s submarine force.