Lieutenant-Commander Monty Davenport, who died on April 14 aged 94, crafted crucially important deception plans for naval intelligence during the Second World War, notably helping to bamboozle the enemy during the landings in North Africa and on D-Day.

In September 1939 Davenport was about to start research in pharmacology when he was called up into the Royal Naval Volunteer Reserve and, on the strength of his scientific training, was appointed – alongside other volunteers such as Ian Fleming – to reinforce the Naval Intelligence Department, under Rear-Admiral (later Vice-Admiral Sir) John Godfrey.

Working directly to Paymaster Lieutenant-Commander (later Captain) DA Wilson in NID section 10, Davenport scrutinised British wireless traffic for mistakes in ciphering and coding, in order to estimate the possibilities of compromise by the Germans. In just two months Wilson’s team produced a report which convinced the authorities of the need to strengthen the crypto-security of the Fleet.

Davenport was not always trying to prevent communications from being intercepted, however, and early in 1940 he took responsibility for encrypting messages into a code which it was known the Italians could read; the intention was to sap Italian morale by portraying them as a liability to their German allies.

In late 1940 Davenport was lent to “Ginger” Boyle, the Earl of Cork and Orrery and Admiral of the Fleet, to secure communications networks for a defence of the Shetland Islands against a German invasion, then thought likely.

Then, during 1941-42, Davenport instigated a signals deception plan to protect convoys in the Mediterranean; this contributed to the successful planning and execution of Operation Torch, the Allied landings in North Africa. He subsequently served in the headquarters established in Algiers.

He was behind further deception schemes the following year. A typical operation was carried out through a combination of faked wireless traffic and agent reports, causing both German and Japanese intelligence to believe that there were two British aircraft carriers in the Indian Ocean, when in fact there were none.

A “deployment” via the South Atlantic of the carrier Indefatigable, which was in fact building on the Clyde, was projected to the enemy entirely by wireless traffic. After “joining” the British East Indies Fleet, the ghost carrier “returned” to the Clyde for an imaginary refit, when her identity was merged with the real Indefatigable after the actual ship was ready for commissioning.

Davenport was promoted lieutenant-commander at the age of 26, and in 1944 made an important contribution to the success of the Allied deception operations ahead of the Normandy landings. In particular, he helped cloak the existence of troopships delivering American forces to Britain prior to D-Day; the operation was so successful that very few ships and men were lost in the Atlantic crossing.

Montague Davenport was born at Teddington on May 26 1916, son of the maritime painter and businessman Hayward Davenport. He was educated at Sherborne, and studied Pharmacy at Chelsea Polytechnic and at University College Hospital, graduating in 1939.

After the war Davenport continued his career in intelligence, as one of the British experts sent to Flensburg, Germany, to interrogate their German counterparts who had been responsible for decoding British signals.

On demobilisation he joined GCHQ, where he assumed responsibility for the security of British government communications. One of his early tasks was to vet Sir Winston Churchill’s History of the Second World War to ensure that the publication in plain language of Churchill’s wartime signalled messages did not compromise any codes still in use, or any other messages.

During the 1950s he advised various colonial governments on setting up their own communications security and, during the planning stage for the invasion of Suez in 1956, prepared complex and delicate deceptions; these were most probably directed at Britain’s own ally in Washington, and in all likelihood concerned the timings of the landings. He was appointed OBE in 1959.

In the same decade Davenport was diagnosed with multiple sclerosis but, supported devotedly by his wife, he fought it and continued his life as normally as possible. His uncomplaining battle with MS lasted more than 50 years, during which time he led a notable campaign for wheelchair access to public buildings.

Throughout the 1960s and 1970s, Davenport developed close relations with his counterparts at America’s National Security Agency (NSA), forging a unique link in the postwar special relationship. He was appointed CBE in 1972 for his contribution to Anglo-US relations.

In spite of being confined to a wheelchair from 1972 onwards, Davenport was director of GCHQ’s London office from that year until his retirement – on the ground of age, not illness – in 1976. Afterwards he collaborated with Professor Harry Hinsley of St John’s College, Cambridge, on the official history of British intelligence.

He combined his career at GCHQ with the management of the family pharmaceutical firm, JT Davenport, founded in 1856, which had built its fortune on Collis Browne’s Chlorodyne, an anti-cholera preparation. He was also director of two other long-established companies, Barclay Pharmaceuticals, and the mineral water and soft drinks manufacturers Camwal. He was elected a Fellow of the Pharmaceutical Society in 1954.

A keen yachtsman and golfer in his earlier life, Davenport never allowed his illness to affect his energy and good humour. His doctors regarded him as an extraordinary and exceptional example of determination and longevity.

Monty Davenport married, in 1952, Olive Brabner. She died in 2008, and he is survived by their two sons.

© Telegraph 16 May 2011