John Douglas Rennie was born on 10 May 1888, the son of Andrew George William Rennie and Elizabeth Wilson Douglas Hope Rennie (neé Hope). He was educated at Glasgow Academy from 1896 to 1904, following which he was apprenticed to William Beardmore and Co., Ltd from 1904 to 1909, during which time he attended the Royal Technical College from 1906 to 1909. Following the completion of his apprenticeship, he continued with Beardmores for another year, engaged in the design of propelling machinery for ships, before attending Glasgow University from 1911 to 1912.

From 1913 to 1914 Rennie was employed, firstly, by the London and Glasgow Iron Shipbuilding and Engineering Co. Ltd., then the Fairfield Shipbuilding and Engineering Co. Ltd., both in Glasgow. Following the outbreak of WWI, Rennie joined the RNVR on 8 March 1915 with the acting rank of Lieutenant, being at first appointed to HMS Kingsnorth, before being assigned to the Supermarine Aviation Co. on 1 December that year, where he was involved with the design and construction of flying boats.

On 1 April 1917 Rennie was assigned to the Air Board and became Technical Assistant at the Royal Aircraft Factory, Farnborough, before transferring as Chief Technical Officer, Seaplane Experimental Station, Felixstowe, working under J.C. Porte on the design of the Felixstowe flying boats. Rennie transferred to the RAF on its formation in April 1918 with the rank of Captain, being promoted to Major on 29 December that year. He was transferred to the unemployed list on 18 July 1919. In 1923 Rennie joined the Blackburn Aeroplane and Motor Co., Ltd. as chief seaplane designer, where he was initially responsible for the wooden floats for the company’s Dart and Velos aircraft. These were considered amongst the best in the world at the time for their clean running, ease of unsticking and smooth alightling. He was then given the challenging task of designing first wooden, then metal, hulls and floats for the Iris flying boats.

Rennie’s most unique design, covered by patent 433925, was the B.20 fling boat with its retractable pontoon float that formed the planing hull.

Rennie was to remain Blackburn’s chief flying boat designer until their last of this type, the B.49 Clydesman of 1945. Rennie resigned from Blackburn in April 1946.

John Douglas Rennie died in Hove, Sussex, in the third quarter of 1971.

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