The flying boom provides a higher fuel transfer rate than probe and drogue and the KC-135 was originally intended to support primarily the B-47 and B-52 fleets. By the time the B-47 was withdrawn, the ratio of KC-135 to B-52 was around 1:1. Presumably, the USAF decided at the time that it only wanted one system and therefore the flying boom system was specified for fighters. Since then, some KC-135s have been fitted with Flight Refuelling Ltd Mk 32b pods as well and a probe and drogue adaptor can be fitted to the flying boom to support USN, USMC and other nation missions.