Possible Clues:

• Revolutionary ship worker can be useful as a pawn?
• One whose position is determined by the rank and file
• Shem's burst in to preserve one of a pair of rooks, maybe
• Rook or pawn, e.g.
• Church converted manses for an ivory castle, say
• King or queen
• Church converted manses for bishop, say
• Eg, bishop, knight
• Piece of board or tin protecting border around vessel
• Playing piece