For a similar example, see Frank Britton, English Delftware in the Bristol Collection, London, 1994, p. 147, no. 10.22. Also see fig. 12 for a strikingly similar engraving of Admiral Keppel published 1779 and now found in the British Museum (126.96.36.1993).
Viscount Keppel became Commander-in-Chief of the British Grand Fleet in 1778 and First Lord of the Admiralty in 1782.