the u. s. army gave the five c-75s back to twa in 1944. twa sent them back to boeing to be rebuilt. boeing replaced the wings and put in more powerful engines. the electrics were replaced with electrics from the boeing b-29 superfortress. after these changes, the 307 could carry 38 passengers. twa switched to the lockheed constellation, but the 307s were used until april, 1951.