The merits of waterjet propulsion systems are increasingly appreciated by designers and operators of vessels with semi-planing and planing hulls, catamarans and rigid sidewall hovercraft for ferry, leisure, work and crew boat roles. The obvious advantage in shallow draught service has reportedly been supplemented in higher speed applications by benefits in fuel economy, machinery cost, manoeuverability, and noise and vibration levels. This article discusses principles of operation, and applications.