Henry was born on 20 July 1900 in Rotherthithe, St. Olave, London, to parents Henry John and Harriet Louisa (née Lockwood) Knapp who had married in the Summer of 1899. In 1901 they were living  with Dad’s parents at 60, Old Road, Rotherhithe, St. Olave, Southwark, London & Surrey. Sadly, in the winter of 1903 the father Henry John died just after the family had moved to West Ham, Surrey. The mother Harriet Louisa then met and married Harry Bradfield Harris 3 years later in 1906 back in the old parish of St.Olave. In 1911 Census Henry J Knapp has had a name change to Harris and is recorded as the son to the head of the house Harry B Harris. The family had moved again and were now living at 80, Etta Street, Deptford, S E London & Kent.

Henry decided to use his birth name Knapp when entering the Royal Navy on Saturday 29 January 1916 as a Boy Second Class aged 15 years and 6 months.  He boarded HMS POWERFUL, a Boy Training Ship berthed in Devonport, for four months basic training after which he transferred to HMS GANGES in Shotley, Suffolk. on 16 May 1916 where he qualified  for Boy Telegraphist on 3 July.  On completion of training he received a draft on 19 October 1916 to HMS VICTORY for three weeks and left on the 8 November to cross the water to HMS DOLPHIN where he was promoted, according to his service documents, to Acting Telegraphist Submarines on the 9 November. A month of branch training completed, on the 6 December he had a draft to HMS LUCIA anchored in the River Tees estuary and joined the 10th Submarine Flotilla based at Tees Port. After completing 11 months on LUCIA books he was advanced to Telegraphist on the 20 December 1917.

He was on board G8 when in company with G12 and escorted by the destroyer HMS MEDEA they exited the Tees and headed East for a patrol area in the Kattegat/Skagarrak area between Denmark and Sweden. G8 was not seen or heard from again.

In 2019 a national survey of wrecks undertaken for “Sea War Museum Jutland” noted a wreck North of Hirtshals in the Skagerrak and a ROV (Remote Operated Vehicle) was deployed to investigate. The wreck was identified and confirmed as G8 with her bow pointing West towards UK and her planes set in the rise position. There is no discernible damage to the hull and it is surmised that G8 was leaving the Kattegat on her way home when a disasterous incident occurred .The vessel and her 32 man crew were declared lost on 14 January 1918. On the service documents of Telegraphist Knapp the D.D. (Discharged Dead) date has been changed by a pen from 14 January to the 3 January while the document was held by the Admiralty.