By this time, his personal Sopwith Camel (serial no. B6313) had become the most successful fighter aircraft in the history of the RAF, Barker having used it to shoot down 46 aircraft and balloons from September 1917 to September 1918, for a total of 404 operational flying hours. It was dismantled in October 1918, Barker keeping the clock as a memento, although he was asked to return it the following day. During this time Barker trialed a series of modifications to B6313, to improve its combat performance. The Clerget rotary engine's cooling efficiency was poorer in the hotter Italian climate, so several supplementary cooling slots were cut into the cowling. The poor upward visibility of the Camel resulted in Barker cutting away progressively larger portions of the center-section fabric. He also had a rifle-type, notch and bead gun-sight arrangement replace the standard gun sight fitting.