Cold case murder detectives are working alongside Royal Gibraltar Police in the search for missing Royal Navy sailor Simon Parkes.
A week-long search of Trafalgar Cemetery in Gibraltar is continuing after new information emerged in the case.
Mr Parkes, a radio operator from Bristol, was 18 years old when he was last seen on 12 December 1986.
More than three decades on, police are searching Trafalgar Cemetery, after "credible" information from a former shipmate came to light.
He went ashore after his ship, HMS Illustrious, docked in Gibraltar.
Mr Parkes told others at The Horseshoe pub on Main Street that he was leaving to get food - he was never seen again.
The pub is popular with the Navy, and is just a short walk away from Trafalgar Cemetery in the centre of Gibraltar.
Acting on information provided by a former shipmate, Detective Inspector Roger Wood, Hampshire Constabulary, is leading the search for remains of the sailor.
"We haven't found any remains as of yet, the search is progressing well," he said.
"What's been particularly positive has been the public response.
"We've had a number of members of the public, both in the UK and in Gibraltar... provide further lines of enquiry which we are following up."
A search was launched when Mr Parkes originally went missing, with some suggesting he may have been involved in an accident or gone absent without authorised leave.
Failed efforts to find Mr Parkes were followed by a Gibraltar-wide search in 2003.
The investigation is being treated as a murder inquiry, though other possibilities are also being considered.
Detective Chief Inspector Brian Finlayson of the Royal Gibraltar Police said: "We've had many incidents out at sea... where people do go missing.
"But for someone who's land-based to go missing entirely, I can't think of any other case."
Anyone with information relating to the investigation can call 101, quoting 'Operation Thornhill', or can do so online by visiting this link.