The next variant ordered was the RC-135B, to be used as an electronic intelligence aircraft to replace the Boeing RB-47H Stratojet, a SIGINT platform. Unlike the earlier variants, the RC-135Bs had Pratt & Whitney TF33 turbofans rather than the older J57s. These ten aircraft were delivered directly to Martin Aircraft beginning in 1965 for installation of their operational electronics suite. By 1967, they emerged as RC-135Cs and all entered service that year. The refueling boom was not fitted and the boom operator station was used as a camera bay for a KA-59 camera. Externally, the aircraft were distinguished by the large “cheek” antenna fairings on the forward fuselage.