Because water and air present similar challenges in control, stability, electronics, hydraulics and propulsion, Boeing began adapting many systems used in jet airplanes for hydrofoils in the 1970s. Boeing launched its first passenger-carrying waterjet-propelled hydrofoil, the JETFOIL, in April 1974. It could carry from 167 to 400 passengers. Boeing built nearly two dozen JETFOILs for service in Hong Kong, Japan, the English Channel, the Canary Islands, Saudi Arabia and Indonesia.