The report presents the results of an analysis of resistance data for twin-screw forms which have been run in the St. Albans and Dumbarton tanks during the 15 years up to 1966. The results are given as tables and charts of ©SN for ships 400-ft LBP by 55-ft breadth moulded by 18-ft draught moulded, with block coefficients from 0.48 to 0.64 and speed-length ratio from 0.750 to 1.500. The values represent the best modern attainment at the time of the analysis (1966).