The Defiant actually made a very effective night interceptor against German bombers until superceded by first the Bristol Beaufighter and then the De Havilland Mosquito. Even the Germans copied the tactic that Defiant nightfighter crews employed of flying below the target aircraft and firing up into it's undefended belly. Granted it only saw limited success in daylight (especially once the Germans worked out how to differentiate it from a Hurricane), but it was never intended for fighter v fighter combat.
However, the Battle just got shot down wherever it went because it was too slow, cumbersome and poorly armed (one forward-firing machine gun and another on a flexible mount).
O L Leigh
The Blackburn Roc had the same gunnery arrangement as the Defiant, and that was pretty much useless. It was a naval fighter that started off as a dive-bomber, the Blackburn Skua, to which they added a rear turret. It could keep up with a Heinkel with the guns aimed dead aft, but as soon as it drew alongside to fire, the gunner would swing the guns out, produce masses of drag, and the Heinkel would get away. It only ever shot down one aircraft, a Ju-88 (which was impressive), and that was with help from a couple of Skuas. Skuas could fight at a pinch, and did an awful lot better than the Roc, because they had forward-facing guns. They were still horribly slow, and ended up being replaced by Fairey Fulmars, developed from (of all things) the Fairey Battle. These had Merlin engines and more guns, making them faster and more effective.
Still, we have a new candidate for Britain's most useless WWII fighter, the Blackburn Roc. Putting all the guns in the turret was never going to be a good idea, especially in a day fighter. When it also happens to be very, very slow, it's pretty much useless.
