A computer program has been developed for predicting twin-nozzleaftbody drag and internal nozzle performance for fighter type aircraft having twin buried engines and dual nozzles. The program is capable of generating the installed thrust-minus-drag data required for conducting mission analysis studies of aircraft of this type. The configuration variables which can be analyzed include 1 nozzle type convergent flap and iris, convergent-divergent with and without secondary flow, and shrouded and unshrouded plug, 2 nozzle lateral spacing, 3 interfairing type horizontal and vertical wedge, 4 interfairing length, and 5 vertical stabilizer type single and twin. The performance prediction methods incorporated in the program are based almost entirely on empirical correlations. Specifically, correlations used in conjunction with one-dimensional flow relationships are employed for the prediction of the nozzle thrust and discharge coefficients, and correlations of the test data obtained during the contracted effort are employed for prediction of the aft-end drag. The prediction methods account for the effects of nozzle pressure ratio and flow separation on both internal and external nozzle surfaces. This manual describes the operation of the computer program in terms of program input requirements, performance prediction methods, and output format and includes a presentation of sample inputoutput cases and a complete computer listing of the program. The program has been developed for use on the CDC 6600 computer.