Silver boatswain's call used after the Battle of Copenhagen, 1797.

The call has a barrel-shaped buoy decorated with a rosette on each side. It has an upward-curving gun with three rope-pattern bands and another at the mouthpiece. The keel has diagonal wrigglework decoration and a scroll end. A short silver chain runs through the metal ring in the keel. The keel is inscribed: 'E.O'Brien to T. Roach 1797'.

On 12 October 1797, the day after the Battle of Camperdown, the 'Monarch' Captain E. O'Brien, flagship of Sir Richard Onslow, 2nd in Command, stood under the stern of Duncan's flagship the 'Venerable' and started three cheers, which were taken up by every ship in the fleet. The signal was given on this call.

The boatswain's call has a long history both as a symbol of office and as a practical instrument for conveying orders at sea. Its distinctive shape has remained practically unchanged from medieval times to the present day. The call's shrill whistle can be varied in pitch to convey a variety of information, and can be heard above the sound of wind and sea. Such instruments were private possessions rather than official equipment and silver calls like this one made suitable gifts and presentation pieces.