 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 . Avro vocally objected on the grounds that neither of these were even in testing at that point , whereas both the MX @-@ 1179 and Falcon were almost ready for production and would have been nearly as effective for " a very large saving in cost " . The Astra proved to be problematic as the system ran into a lengthy period of delays , and when the USN cancelled the Sparrow II in 1956 , Canadair was quickly brought in to continue the Sparrow program in Canada , although they expressed grave concerns about the project as well and the move added yet more expense . 
