 Powered by Pratt & Whitney JT4A turbojets, the 707-320 entered service in 1959, and the with Rolls-Royce Conway turbofans in 1960.The 720, a lighter short-range variant, was also introduced in 1960.Powered by Pratt & Whitney JT3D turbofans, the 707-120B debuted in 1961 and the 707-320B in 1962.