On homeward flight all four engines cut, the fuel tanks having been holed by flak. Aircraft ditched in North Sea. Spotted by a Hudson at 1330 hrs on 22nd. Crew picked up by Launch later and landed at Yarmouth having spent 15 hours in the dinghy. Pilot and Nav moderately injured, Flt Eng and Bomb Aimer mildly injured. None admitted to SSQ or Hospital.