 The -120B had the wing modifications introduced on the 720 and a longer tailplane; a total of 72 were built, 31 for American and 41 for TWA, plus six short-bodied -138Bs for Qantas.American had its 23 surviving -123s converted to -123Bs, but TWA did not convert its 15 -131s.The only other conversions were Pan American's five surviving -121s and one surviving -139, the three aircraft delivered to the USAF as -153s and the seven short-bodied Qantas -138s.