HMS Triumph is in Gibraltar after arriving on Friday to restock supplies and munitions.
The vessel is berthed at the Naval base.
Triumph is the last remaining Trafalgar-class nuclear submarine in the Royal Navy fleet.
The 23 year old sub was involved in military operations in Afghanistan and Libya, and described as having a varied role that includes fleet protection and intelligence gathering.
She is equipped with cruise missiles and Spearfish torpedoes and is understood to have taken on munitions while on the Rock.
The MOD does not comment on submarine movements in Gibraltar waters.
HMS Triumph can stay at sea unsupported for up to three months, and in 1993 sailed to Australia, travelling 41,000 miles unsupported – the longest solo deployment ever completed by a Royal Navy submarine.