In July 1953, the proposal was accepted and Avro was given the go-ahead to start a full design study under the project name: "CF-105". In December, CA$27 million was provided to start flight modelling. At first, the project was limited in scope, but the introduction of the Soviet Myasishchev M-4 "Bison" jet bomber and the Soviet Union's testing of a hydrogen bomb the next month dramatically changed Cold War priorities. In March 1955, the contract was upgraded to CA$260 million for five Arrow Mk.1 flight-test aircraft, to be followed by 35 Arrow Mk. 2s with production engines and fire-control systems.