Possible Clues:

• Carlsbad attraction
• Large underground hollow
• Beware of the British Navy as a whole, by the sound of it
• Can one get around to get the priest to turn up for the underground?
• Beware of the British Navy - it may be at the coast (6)
• Many swear and a quarter get into a hole
• Large 24 chamber
• Claim to be hollow in down there
• Craven in a cave
• Claim to be in a hole in the ground