Admiral Sir Sydney Colpoys Dacres GCB (1805 – 8 March 1884) was an officer of the Royal Navy who saw service during the Greek War of Independence, when he was involved in an attack on the Turkish forces at Morea, and later during the Crimean War. Born into a substantial naval dynasty during the Napoleonic Wars, he eventually rose to the rank of Admiral and became First Naval Lord. His only significant action as First Naval Lord was to press for the abolition of masts. He went on to be Visitor and Governor of Greenwich Hospital.