Making use of an ensemble of computer codes, Hughes Electron Dynamics (HED) has achieved first pass design success in the development of slow wave circuits for several traveling wave tubes (TWTs) during the last year. By first pass design success we mean that when tested, the first device fabricated achieved the design goals for RF output power, basic efficiency, gain and phase shift. The design goals are derived from the predictions of a computer model based on the exact dimensions of the TWT. This accomplishment has enabled HED to significantly reduce the time required to develop new devices and demonstrate new design concepts. The design procedure is based in part on a computer model that produces accurate values of the dispersion and interaction impedance from the exact dimensions and electrical properties of the materials that make up the slow wave circuit. The authors of this earlier work demonstrated that this procedure produces an accurate analysis of existing circuits; the material presented here describes the successful application of this procedure to TWT design.