One of the old boys in the Aircrew Association told me about "Village Inn", a radar controlled rear gun system that replaced the rear gunner in some Lancasters back in 1944.
To start with it slaughtered the German night fighters but then they worked out why other Lancs that came up from behind didn't get fired on. Looking through the rather too plentiful piles of Lanc wrecks they found that they were fitted with Infra-red lights in the nose that flashed coded signals to the receivers identifying them as friendly.
The Germans kitted out their night fighters in a similar fashion and solved the problem (for them at any rate).