Fast and accurate radiative transfer models and their adjoints are a requirement for the assimilation of satellite observed radiances into numerical prediction models. Informal tests over the past few years have suggested that the Optical Path Transmittance (OPTRAN) code performed better with channels sensitive to water vapor, and the Rapid Transmittance TOVS (RTTOV) performed better with temperature sounding channels. The author spent the summer of 2001 as a visiting scientist at the MetOffice in Bracknell, UK. The purpose of this visit was to merge the basic components of the two codes and test whether the combined code improved results compared with the individual codes. This paper reports on the results of this test.