Cowburn was born on March 3, 1909. He had arrived in Paris, aged eight with his parents, and studied at a British school in Boulogne-sur-Seine and then at a Lycée. He later studied electrical engineering and worked for the American firm, Foster Wheeler, building distillation plants for oil refineries all over France. He was a fluent French speaker. He was married to a Frenchwoman. Due to his knowledge of the oil industry in France, he was seen as an excellent acquisition for the Special Operations Executive.
Wartime activities
Recruited in 1941 into SOE's 'F' Section, Cowburn was trained at Wanborough Manor in the Spring of 1941.
First mission
Cowburn first parachuted into Vichy France from a Whitley bomber on 6 September 1941 with Pierre de Vomécourt. His mission was to obtain information on the best targets for the sabotage of oil and fuel stocks. While in France he got tangled up in the delicate dance between Vomécourt and double agent Mathilde Carré and attempted to return with them to Britain by boat. Failing in that, he returned to Britain in March 1942 via Spain after crossing the Pyrenees on foot.
Second mission
On the night of 1/2 June 1942, Cowburn parachuted from a Halifax bomber and provide direction for the French Resistance TINKER circuit in the Indre area. With the help of Augustus Chanteraine, Cowburn organized the reception of two airdrops of weapons and explosives that equipped the first resistance group in that area. He also conducted several sabotage missions, including the power lines from the power plant to Éguzon and disrupted production at the Bloch aircraft factory at Chateauroux by tampering with the machine tools. He returned to Britain in a Lysander on 26 October 1942.
Third mission
Cowburn's third mission was to be his most important. Parachuting again from a Halifax bomber on 11 April 1943, Cowburn now took control of, and managed the TINKER circuit from Troyes, the capital of the Aube departement. Cowburn reviews the intelligence gathering in the area and builds up detailed information for a commando-style attack on marshalling yard in Troyes. On the night of 3/4 July 1943, along with other resistance members seriously damage a number of locomotive engines, several of which are put out of commission for several months. He returned to Britain once again in a Lysander on 17 September 1943.
Fourth mission
Cowburn's final mission was to set up a new Resistance cell near Amiens. Arriving by parachute on 30 July 1944 he was also looking to see if he could intercept two fellow SOE agents arrested by the Germans. He was unable to locate the agents and shortly after allied forces liberated France in August 1944 he returned to the United Kingdom.