The propellers were driven directly by the turbines, for sufficiently robust gearboxes had not yet been developed, and became available in only 1916. Instead, the turbines had to be designed to run at a much lower speed than those normally accepted as being optimum. Thus, the efficiency of the turbines installed was less at low speeds than a conventional reciprocating (piston-in-cylinder) steam engine, but significantly better when the engines were run at high speed, as was usually the case for an express liner. The ship was fitted with 23 double-ended and two single-ended boilers (which fitted the forward space where the ship narrowed), operating at a maximum 195 psi and containing 192 individual furnaces.