Royal Naval Reserve divers have been practising how they search and clear the seabed of explosives at an exercise in Portland, near Weymouth.
It's a skill that is currently being used in ports like Bahrain where Royal Navy ships are deployed, and was used during the London Olympics and in Iraq.
Before conducting a search the divers mark out the area.
Commander Stuart Robertson says they would be deployed to search areas around vessels for ammunition or mines.
"Once the ship has come alongside we may be asked to search that ship twice or three times a day - both day and night, in order to make sure nothing has been put on the side of the ship to damage it or harm the people onboard."
Before entering the water they have to methodically check all of their kit.
Petty Officer Alistair Jackson, Supervisor of the Royal Naval Reservists said: "A diving set is a life support system and its a lot to put to memory so what the Armed Forces do is they put together a maintenance log which goes through a system that allows you to make sure all of those pre-dive checks, that support life in the water, happen."
"We want to be as slick as possible to give the Captain and the crew the thumbs up that the ship is clear."
The reservists get together once a month to go over the skills that could keep them alive.
On this exercise, they were going over emergency operating procedures that looked into what to do when a diver or their companion gets into trouble in the water.
The searches they were practising mirror how they would react in a real situation.
Sub Lieutenant Aaron Barrett, a Royal Naval Reservist says the role gives them a chance to break away from civilian life.
"There's a lot of interesting and dynamic tasks you can get involved with that are unthinkable if you live on the civvy side."