Green Satin was a doppler radar system developed by the Royal Air Force as an air navigation aid. The system provided direct measures of the drift speed and direction, and thereby allowed accurate calculation of the winds aloft. It was originally specified for the English Electric Canberra bomber, and subsequently used in a number of other aircraft, including much of the V bomber fleet. The name comes from an era when the Ministry of Supply used random combinations of colours and code words to prevent their code names being too literal. A version known as Blue Silk with lower top-speed limits was used in some marks of Canberra and by the Royal Navy..