Mystery surrounds the disappearance of radio operator Simon Parkes who vanished at the age of 18 on the day aircraft carrier HMS Illustrious put in at the British Overseas Territory on December 12 in 1986.
Despite previous police searches in Gibraltar his disappearance remains unsolved.
A police investigation was launched in 2001 after the conviction of Petty Officer Allan Grimson, who served on Illustrious at the same time as Simon, who confessed to killing two young men in Portsmouth.
Today sees the start of a week-long operation after a new witness told police of credible new information.
Simon’s mum Margaret Parkes, 73, told The News: 'It's been 20 years since the last investigation and this time our hopes are that his remains are found and that we can bring him home.’
Leading investigator Detective Inspector Roger Wood told The News a search at Trafalgar Cemetery will be carried out ‘hopefully to locate the remains of Simon Parkes’.
It’s understood the cemetery was searched around 20 years ago but DI Wood said his team was ‘duty bound’ to return as previous investigators ‘weren’t in possession of what we’re in possession of today’.
The homicide detective said: ‘A new witness has come forward with significant information which we have assessed and found to be credible.
‘On the back of that today in Gibraltar we are beginning an operation which will see us carry out further enquiries and specifically searches around the location called the Trafalgar Cemetery in Gibraltar.
‘It's a small but historically significant location in Gibraltar and our information leads us there.
‘So in conjunction with the Royal Gibraltar Police and other partner agencies we're carrying out a week-long operation doing some proportionate searches within that cemetery, hopefully to locate the remains of Simon Parkes and answer finally what happened to him, and who if anybody is responsible for his disappearance.'
The cemetery - where some of the dead from the Battle of Trafalgar are buried - is a short walk south from the Horseshoe Bar where Simon was reportedly seen with killer Grimson.
Grimson, 60, is serving a 22-year sentence imposed in 2001 for the brutal murder of two young men in Portsmouth, aged 18 and 20 when he killed them a year apart on December 12 in 1997 and 1998.
Two forensic anthropologists, experts in human remains, are among the nine-strong Hampshire police team in Gibraltar today.
Scenes of crimes officers are also in Gibraltar poised ready to preserve any uncovered evidence that could be used to bring anyone responsible to justice.
DI Wood told this newspaper: ‘We are cautiously optimistic. We hope for a good outcome in that we hope we will find Simon's remains and be able to start answering the questions of what happened to him and ultimately who, if anyone, was responsible for his disappearance.
‘But we must temper that with the possibility that we won't be successful, then simply what we will continue to do is review our lines of enquiry and anything considered to be reasonable will be followed.
‘In cases like this the police never stop working on them, when information comes to light that generates viable and reasonable lines of enquiry we would seek to take them forward.’
He added: ‘We're hopeful that we're right and the information is going to lead us to answer the questions. But that hope is tempered with the reality we could be in a week's time wrapping up the operation having not found Simon's remains.’
The Royal Navy and RAF are on standby if needed to assist, it's understood.
DI Wood said: ‘There will certainly be further enquiries based on information and things that we have generated as a result of resurrecting this cold case.’
Both Bristol-based retired teacher Mrs Parkes and her husband Dave, 77, are poised ready to fly to Gibraltar should Simon’s remains be found.
'We have every faith in the investigation,’ Mrs Parkes said. 'We've done a lot of waiting over the years.’
Investigators will seize the chance to make other enquiries while in Gibraltar.
They are keen to speak with anyone who saw something ‘odd or unusual’ on the night Simon's vanished, and with HMS Illustrious crew who have not spoken to police ‘no matter how small’ the piece of information they may know.
Police have not commented on links to Grimson.