HMS Ocean's security exercise is part of Olympic Guardian

HMS Ocean's security exercise in preparation for the Olympic Games is the final phase of the operation named Olympic Guardian, which began earlier this week in Weymouth and in the airspace over the capital. The ship will act as a launch pad for helicopters and a base for Royal Marine snipers.

Smaller crafts and patrol boats will accompany the ship as part of the maritime security plan. The snipers have extensive experience of shooting the engines of fast vessels in the Royal Navy's fight against the drug trade in the Caribbean.

Ocean will travel up the Thames before attempting a complicated 180-degree turn as it reaches its destination. The warship is 38 metres wide, and Captain Andrew Betton will carefully guide it through "challenging" gaps of just 60 metres.