Radar Altimeter in WW2
Can someone please give any info about the use of radar altimeters in WW2?
I know that they were employed in heavy bombers during WW2 and in smaller aircraft during the Korean War (late models F4U, F9F...), but I want to know when was it first used in combat aircraft, and some details about its use on smaller aircraft - single engined fighters and smaller twin engined aircraft like Mosquito and A/B-26 Invader. Especially Mosquito.
I am asking here because this topic seems to be very thinly covered around the Internet.