In the course of 1936 John left Airwork, having been appointed Assistant General Manager of the De Havilland Aircraft Company, where he remained throughout the Second World War, later becoming joint General Manager of the Engine and Airscrew Divisions.
This career move to a managerial position was a major change from flying around the Middle East. His arrival coincided with the period in which the company was stepping up its production in response to the government’s policy of rearmament. At the end of 1936 he was transferred from the Hatfield factory to the original parent factory at Stag Lane to take charge of the manufacture of the thousands of Gypsy Major trainer engines needed to power the Tiger Moth trainer and other aircraft required by the RAF expansion programme. Simultaneously, the company was expanding its production of the Hamilton Standard Propeller under licence from the U.S.A. His specific responsibility was managing engine and propeller production at the Stag Lane and Lostock factories.
Propeller production had started at the Stag Lane factory in July 1935 and in November 1937 the company embarked on building a second “shadow” propeller factory at Lostock near Bolton, Lancashire. Up to 1939 these factories produced propellers for both civilian and military use and before the war had even begun they had delivered 10,000 for 20 different aircraft types. In the run-up to the war all new RAF planes were fitted with De Havilland propellers. In the course of the war 77,029 propellers were produced by the Lostock factory and 23,210 at Stag Lane. In addition, 37,801 propellers assembled from American components were made at Lostock. As production expanded to a network of shadow factories, John was in the end responsible for 15,000 workers in fifteen different factories. Many different types of propeller were made, to be fitted to over forty different types of aircraft. John assisted in the test flying of a variety of aircraft to provide improved performance in relation to propeller design.
The propeller factories made a crucial contribution to the success of the RAF in the Battle of Britain. In early June 1940 test flights with constant-speed operation propellers (in which John took part) had shown that they could greatly improve the performance of the Spitfire and the Hurricane. In the period between June 25th and August 16th 1940 De Havilland worked flat out to convert 1,051 Spitfires and Hurricanes to constant speed propellers. This required both manufacturing and fitting the conversion sets at top speed – just in time to enable them to fight much more effectively against the Luftwaffe’s mass attacks on Channel ports and shipping. In February to March 1944 he made a two-month business trip to Canada and the USA on behalf of De Havilland, for the purpose of visiting propeller and aircraft engine factories (including their own factory in Canada), comparing their products and production with those of De Havilland, acquiring technical knowledge about new developments (such as jet engines), exploring the possibilities of collaboration in propeller and aircraft production, and talking to staff from the American and Canadian Air Forces.
It is easy to imagine the management challenges which wartime production must have involved: rapidly scaling up production volumes, recruiting new staff, replacing skilled employees who left the company to join the Armed Forces, coordinating the work of the two main factories and the network of shadow factories, dealing with the disruption caused by air raids, maintaining staff morale, and incorporating continual technical changes in the production process. Executives worked a seven-day week, with a day off when advisable.
At the outbreak of the war 601 Squadron was incorporated in the R.A.F. but John, while retaining his commission as an R.A.F.officer, was not called up to fight because his role as a manager at an aircraft manufacturing company was thought to be more important. After the war he continued to maintain friendships with various people he had known through the squadron and participated in various commemorative events, such as the thirty-second annual dinner of the Old Comrades Association in March 1957, prior to the disbandment of the Squadron. He proudly paraded in lounge suit and bowler hat when the Squadron received a new Standard from Prince Philip in July 1954 and attended the celebrations for the 50th Anniversary of the formation of the Royal Auxiliary Air Force in October 1974. He remained a lifelong member of the R.A.F. Club and of the Aero Club which he visited regularly when in London, meeting his old friends.