J.E. "Johnnie" Johnson was the famous commander of the all-Canadian Kenley Wing,which became one of the RAFs top units while under his leadership. In his book Wing Leader, he wrote the following regarding his first impression of the Mk.IX: "She seemed very fast, the engine was sweet and she responded to the controls as only a thoroughbred can. I decided that she should be mine, and I never had occasion to regret that choice." The Mk.IX flown by Johnson featured the code letters "JEJ," his personal initials.