Fourteen Royal Navy divers are attempting to walk 26 miles underwater in kit weighing 40kg for charity. The mine clearance divers from Fleet Diving Squadron at Horsea Island in Portsmouth started the marathon today (Friday) and hope the punishing challenge will raise £5,000 for the Royal Navy and Royal Marines Charity. They will take it in turns – walking in pairs - to complete one kilometre at a time in six metres of water in the giant lake at their base. They aim to complete the challenge in 30 hours. Their equipment includes lead-lined boots, an air cylinder and a 17kg helmet. They will pull a rigid inflatable boat which will carry three support crew and back-up equipment.