You have to be a little wary of StH, at times; the first cannon-armed Spitfires weren't known as Ib, that designation came later. Although there were no .303" guns, the compartments remained, so they could have been refitted if the will was there; the Squadron members were just so disenchanted with the way that the aircraft swung, when a single cannon jammed, that they requested, and got, their original type of Spitfires back. Though the results, when the guns did operate properly, were spectacular, it simply didn't happen often enough. The cause was the jamming of the empty shells, after firing; several different types of feed were tried, but none worked, and it took the Vb's arrival, with a different system, to solve the problem.