She's known as the mother of our modern underwater fleet. And, this week, divers have visited the wreak of one of Britain's very first Submarines.
Lying, upright in 30 metres of water - that's 100 feet - the Holland 5 was one of the first submarines accepted for service by the Royal Navy.
She sank 100 years ago and, to mark the centenary, the Nautical Archaeology Society dived to the site - to monitor her condition. Sarah Saunders went on an exclusive journey with them.
Click below to see the video