In 1936 the RAF issued Specification T6/36 for an aircraft designed from the outset for crew training. At the time, air crew training was often carried out retired aircraft types. T6/36 required the new design be a monoplane with retractable undercarriage, side-by-side seating with dual controls, a radio compartment for the training of navigators and radio operators and a manually-operated gun turret. There was to even be provision for a forward firing gun and practice bomb carriage as well. The RAF indicated that well over 100 aircraft would be required.
De Havilland was selected to built its design, an elegant looking aircraft powered by a single 525-horsepower Gipsy King 1 12-cylinder engine. The De Havilland DH.93 Don made its first flight on 18 June 1937. Initial flight testing showed the need for several modifications, including the addition of auxiliary fins under the horizontal tailplane but an order for 250 aircraft went forth.
Once the training equipment including the gun turret was installed, it was found the DH.93 Don was underpowered and suffered from continued stability issues. The order was revised to only 50 aircraft which were to be fitted out as light transports seating four to six individuals. A "turtleback" was fitted in place of the radio compartment and the dorsal gun turret. Of the 50 aircraft delivered, only 30 were delivered as airworthy and distributed quietly across several RAF station flights. The remaining 20 went straight into service as engineless ground instructional airframes.
The RAF's crew training needs shifted over to a design that was not tendered for the T6/36 specification- the Avro Type 652A first flew the year before the issuance of Specification T6/36 and would go into production as the vastly superior Avro Anson while the DH.93 Don faded into obscurity.
Source: Air Enthusiast, May/June 2003. "Out-Moded Teacher- De Havilland's Don Crew Trainer" by Daniel Ford, p74-75.
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