 In 1955, this engine was also cancelled, leaving the design with no engine.At this point, the Pratt & Whitney J75 was selected for the initial test-flight models, while the new TR 13 engine was developed at Orenda for the production Mk 2s.After evaluating the engineering mock-ups and the full-scale wooden mock-up in February 1956, the RCAF demanded additional changes, selecting the advanced RCA-Victor "Astra" fire-control system firing the equally advanced United States Navy Sparrow II in place of the MX-1179 and Falcon combination.