The police and Royal Navy have outlined their plan to fight the threat of terror attacks at next month's huge International Fleet Review.
A host of warships will be reviewed by the Queen in the Solent
More than 10,000 spectator yachts are expected to attend the event in the Solent, off Portsmouth, Hampshire, which will be carried out by the Queen.
More than 160 ships will be inspected as part of the Trafalgar 200 event.
Minesweepers are already being used to secure the Solent and exclusion zones will be in place around each warship.
Ships and government leaders from 73 nations have been invited to take part in the event on 28 June.
It is marking the 200th anniversary of the Battle of Trafalgar in 1805.
Capt Chris Richards, chief of staff to the commander of the UK maritime force, said on Thursday that the event promised to be a "once-in-a-lifetime" spectacle.
But, at a briefing held at HMS Excellent, Whale Island, Portsmouth, he said careful planning was under way to ensure the safety of all involved.
A total of 250 personnel will be on board the ships and a further 150 in patrol vessels to monitor security.
He said: "It will look pretty jam packed. We have continuing surveillance of the area in and above the water to keep our guard up so no one can do anything illegal in the area before the ships arrive or during the events."
'No specific threat'
Assistant Chief Constable Steve Watts, of Hampshire police, said that his officers were already carrying out random checks on vehicles in the county as part of advance security preparations.
Police hope the campaign will urge people to report suspicious activity
He added: "At this time there is no specific threat to the Trafalgar 200 celebrations but it would be wrong of us and the Royal Navy to ignore the possibility of terrorist preparations and therefore we have contingency plans in place."
A poster campaign was launched on Thursday urging boat-users to report anything suspicious to the police.
Capt Richards said one of the biggest problems was the potential of small craft getting too close to the warships.
He said: "Our main concern is the casual yachtsman who is coming down from his gin palace in London, we want him to be aware of the measures we are putting in place."
The International Fleet Review, which will involve 58 Royal Navy ships, 56 foreign warships, 21 merchant ships, 27 tall ships, will be followed by a Son et Lumiere battle re-enactment.