The crew issued a mayday after hitting an unknown object while on a training exercise in the Bristol Channel on Thursday evening.
Their £40,000 rigid inflatable boat began taking on water near Clevedon, Somerset, at around 8.45pm.
The crew, which included one trainee, alerted Swansea coastguard which dispatched an RNLI lifeboat from Weston-super-Mare, the Severn Area Rescue Association craft from Beachley, and a helicopter.
The lifeboat – which has been operated by the independent Portishead and Bristol Lifeboat Trust for three years – was towed back to its base in Portishead at 9.45pm. No one was injured in the incident.
Crew member Ian Lazenby said: "Our initial thoughts were that we were definitely sinking, that's why we called the mayday.
"We were in three knots of tide, heading west, going dark, would they have found us? That's your first thought, so you just get on with making sure they know where you are."
The boat – which has been launched into the channel 232 times – will out of action for at least two weeks while the damage is assessed.
