The first trijet aircraft entered commercial service in the 1960s. Faced with rising fuel costs, airlines were looking for an aircraft that would be more fuel-efficient than four-engined aircraft such as the Boeing 707. Three-engined aircraft also had the advantage of being certified to fly for longer distances over water than their twin-engined counterparts. Eastern Air Lines, for example, was keen for the US manufacturer to develop an aircraft that it could deploy on its longer Caribbean routes.