Powered by early Pratt & Whitney turbojet engines, the earliest 707s had a range capability that was barely sufficient for the Atlantic Ocean. Boeing quickly developed the larger 707-320 Intercontinental series with a longer fuselage, bigger wing and higher-powered engines. These improvements increased fuel capacity from 15,000 gallons to more than 23,000 gallons, and gave the 707 truly intercontinental range of over 4,000 miles in a 141-seat (mixed class) seating configuration. Early in the 1960s, the Pratt & Whitney JT3D turbofan engines were fitted to provide lower fuel consumption, reduce noise and further increase range to about 6,000 miles.