The reduction of hydrodynamic noise resulting from singing and cavitation was a serious problem in a recent wire-guided high-speed underwater missile development. The noise level of this body not only was sufficiently high to prevent a model of the latest developed sonar from tracking other bodies, but permitted a possible enemy more than sufficient time for successful evasion. The principal noise sources originated from both cavitation and the singing of the missile fins and two counter-rotating propellers. To eliminate the propeller singing, wedges of 40°, 33°, and 25° were applied to the propeller's trailing edges. Only the 25° and 33° angles successfully eliminated the propeller singing. Sanding the critical area of the fins, theoretically determined from the Strouhal number K = fd/v, where f is the frequency, d the body's trailing edge diameter, v the fluid velocity, and K is a constant, eliminated the fin singing without noticeably increasing the cavitation noise level. However, a commercial process was required. Roughening the critical area by sand blasting, or use of a painted, crackle-like finish were unsuccessful. Wedging with an apex angle of 25° succeeded. Flow noise also appeared to be reduced by eliminating cracks, voids, and rough areas. The data obtained also implied that singing (i.e., the Strouhal number) may not be so much a function of the trailing edge depth and its vertical thickness as it is of an effective depth or area forward of this point.