John Blackett (1777/8-1858) was from at least 1814 to 1851 employed by the Ordnance (the government body charged with supplying armaments and munitions), and was based in 1841 and 1851 at Harwich, Essex. He named one of his sons Edmund Phipps Blackett (1830-1887), almost certainly after Hon. Edmund Phipps, (the son of the 1st Earl of Mulgrave), who in 1812 became Clerk of the Deliveries of the Ordnance, a government ministerial position, and held the post until it was abolished in 1830.
It is not clear whether Edmund Phipps had shown a special kindness to John Blackett or whether John bestowed the name on his son in the hope of advancing his own career. If the latter, it appears to have met with only limited success as John is shown as a store keeper for the Ordnance at the baptism of an elder son John Griffiths Blackett in 1814, but was still no more than a clerk there in 1841 and 1851.
Please also see Blacketts of Essex and Cambridge in Can You Help Us?.