His aversion to cannon was also a handicap
The introduction of the cannon during the BoB had dismal results, usually failing after getting off one or two rounds, that may have been the reason for his opinion at the time. Cannon armed squadrons asked for, and received, their .303 aircraft back. It took sometime to get the technical issues sorted, by which time DB was residing in Germany.
http://spitfiresite.com/2010/07/stor...-spitfire.html