Cyril was born on 25 April 1899, the sixth child of John and Catherine Teresa (nee Connor) Jeffery and Baptised on 7 May 1899 in the Cathedral of St. John,Portsmouth. Eventually the family unit consisted of Mum, Dad, 3 brothers and 3 sisters.

On Wednesday 19 May 1915 he joined the RN when he walked over the gangway of HMS IMPREGNABLE the “Boy Training Ship” based in Devonport as a Boy 2c to start six months basic training following the footsteps of his elder Brother John that had 13 years before joined the RN  in 1902. On the 17 July he was made Boy 1c and on the 27 November drafted to HMS VICTORY I staying for 3 months when a draft to HMS MAIDSTONE on 5 February 1916 introduced him to the submarine service. Then on 22 April 1916bhe joined HMS BONAVENTURE still as Boy Ic but on 9 March 1917 he was drafted to HMS DOLPHIN as   Ord. Telegraphist and on the 16 April drafted back to MADSTONE based in Harwich for E 47 part of the 9th Flotilla.

E47 was reported lost on the 20 August 1917 with no survivors from her 32 man crew.

In 2002 a Dutch Diving team pinpointed the wreck site and exploratory dives shows what appears to be mine damage causing large hole on the Port side around the control room area. The bow lies in an Easterly direction, which indicates E 47 was on her way back to base. The deck gun had been ripped away from the deck by fishing net activity and this was salvaged and the serial number identifies the wreckof that of E 47. There were no  surivors from her 32 man crew.