Born at Merstham, Surrey on 9 January 1899, Jefferis was educated at Tonbridge School and Royal Military Academy, Woolwich. From Woolwich he was commissioned into the Royal Engineers on 6 June 1918 and after passing through the School of Military Engineering at Chatham, he was posted to the First Field Squadron RE in the Rhine Army. In 1920 he went to India and served with the Queen's Own Madras Sappers and Miners in the Third Field Troop at Sialkot. In 1922 he went into the Works Services in India as garrison engineer at Kohat and then at Khaisora which is today in Pakistan. He saw active service in the Waziristan Campaign where his main responsibility was the construction of roads. On 12 June 1923 he was awarded the Military Cross, the citation read: He then returned to Chatham and went to Cambridge University. In 1925, he returned to India and was placed on special duty at Kabul in the foreign and political department. In 1926 he returned to Nowshera as garrison engineer and spent several years in Works Services at Peshawar where he made full use of this engineering genius designing bridges. Also in 1925, he married Ruth Carolyne, daughter of G. E. Wakefield. They had three sons, two of whom went on to serve in the Royal Engineers. On 1 June 1929, Jefferis was promoted to captain. In 1934 he was posted to the Royal Bombay Sappers and Miners at Kirkee as a company commander in the training battalion. He returned to Britain in 1936 and joined the Twenty-third Field Company at Aldershot. Moving to the First Field Squadron, he stayed at Aldershot while the unit was being mechanised. While at Aldershot, Jefferis successfully raced horses and played squash competitively. He was promoted major on 6 June 1938, and on 4 April 1939 he was appointed a General Staff Officer, Grade 2.
Jefferis started working on sabotage devices for the "Military Intelligence Research". When MIR was combined with other hush-hush elements to form the SOE, Jefferis' unit was not included and it instead became a department in the Ministry of Defence; the only unit of the Minister of Defence and was known as "MD1", ultimately based in a house called "The Firs" in Whitchurch near Aylesbury in Buckinghamshire England. The unit was responsible for the design, development and production of a number of unique special forces and regular munitions during the Second World War. It gained the nickname "Winston Churchill's toyshop". Jefferis was an explosives expert and engineer, but lacked the ability to manage men well. He was assisted in the management of MD1 by a wily assistant – Major Stuart Macrae, whose book Winston Churchill's Toyshop, is still one of the few published works on this unique unit. Over the period of the Second World War, MD1 was responsible for the introduction into service of a total of 26 different devices. Their designs include the PIAT, the Sticky bomb and one of the first magnetic Limpet naval mines. Through the application of the Squash head and HEAT technology they had a role in the development and production of Lt-Col Stewart Blacker's Blacker Bombard, the PIAT matched to a hollow charge warhead, Hedgehog and tank variants including the AVRE with its "Flying Dustbin" 290mm Petard spigot mortar, and a bridge-laying tank. Jefferis developed the idea of the squash head further. His most ambitious project was a bomb designed to sink capital ships, his ideas were put forward by himself and Lord Cherwell in 1944 and coincided with the Admiralty's interest in developing a homing bomb for use against the Japanese. The development of this weapon was supported by the Air Staff and MAP who allocated it a higher priority that any other anti-capital ship weapon. When the war ended, development of the 'Cherwell-Jefferis' bomb was continued under the code names Journey's End and Blue Boar. Prime Minister Churchill became acquainted with then Jefferis in 1940 and regarded him as a "singularly capable and forceful man." He recommended a promotion to lieutenant colonel so that Jefferis would have more authority. Jefferis received substantive promotion to this rank on 10 February 1944. Jefferis was promoted to Knight Commander of the Order of the British Empire by Churchill in the 1945 Prime Minister's Resignation Honours, having previously been appointed a Commander of the Order. He was promoted to acting major general on 15 May 1945, and substantive colonel on 14 July 1945. He left the Ministry of Supply on 20 November 1945, reverting to the temporary rank of brigadier.
Later career
In 1945, Jefferis became deputy Engineer-in-Chief in India and 1947 he became Engineer-in-Chief in Pakistan, holding the temporary rank of major general. He was promoted to substantive brigadier on 1 November 1947, and returned to England on 2 January 1950 to become Chief Superintendent of the Military Engineering Experimental Establishment, reverting to the rank of brigadier on 8 March 1950. He was made ADC to the King on 24 May 1951 and held that appointment until he retired on 18 August 1953, on his retirement he was granted the honorary rank of major-general. As an ADC, Jefferis took part in King George VI's funeral, and Queen Elizabeth II's Coronation Procession. He died on 5 September 1963.
Ocean racing
Jefferis had a passion for ocean racing. In 1938, he built a 7-ton yacht at Aldershot called Prelude with another Royal Engineer officer and they sailed successfully both before and after the war.
