Two previous attempts at radar-controlled gun-laying were notable. In Britain, the 75 MHz GL Mk. I radar was used in connection with a Vickers predictor; and in the U.S., the 200 MHz SCR-268 was combined with the Sperry M-4 predictor. Neither the US or UK systems had the accuracy needed to directly lay their associated guns, due to their long wavelengths. The US delegates then mentioned the Navy's work on a 10 cm wavelength radar, which could provide the required resolution with relatively small antennas, but their klystron tube had low power and was not practical.