 Bodywork would be of aluminium, rather than steel, but the official drawings showed that they would still be painted red, although experiments with unpainted aluminium R Stock were taking place on the District line at the time.The high cost of building the trains, and a decline in passenger numbers, resulted in the plans being shelved in September 1952.When the situation was re-assessed in 1954, London Underground decided to build three seven-car trains incorporating new ideas, and these became the 1956 Stock.