Admiral Sir William Fanshawe Martin, 4th Baronet, GCB (5 December 1801 – 24 March 1895), was a Royal Navy officer.

As a commander, he provided valuable support to British merchants at Callao in Peru in the early 1820s during the Peruvian War of Independence.

[1] Promoted to captain on 5 June 1824, Martin took command of the sixth-rate HMS Samarang in the Mediterranean Fleet in November 1826 and then went onto half-pay in 1831.

[3] Promoted to rear-admiral on 28 May 1853,[4] Martin became Admiral Superintendent of Portsmouth Dockyard, hoisting his flag in the first-rate HMS St Vincent in November 1853.

[1] Having been appointed a Knight Commander of the Order of the Bath on 28 June 1861[6] and promoted to full admiral on 14 November 1863,[7] he succeeded to the baronetcy on 4 December 1863: this had been conferred on his grandfather, but passed to Martin upon the death of his cousin, Sir Henry, the 3rd Baronet.