An ultrasonic delay line has been developed which employs water as the delay medium and permits continuous adjustment of delay between the limits of 28 and 58 μsec. Adjustment of delay is effected by movement of a corner reflector relative to two crystal transducers whose positions are fixed. The center frequency is 30 Mc and the bandwidth is in excess of 10 Mc. Uniformity of bandwidth and response over this range is controlled by a combination of measures including selection and design of backing and bonding materials, offsetting the resonant frequency of the transducers from the operating band and use of particular alignment techniques. Delay stability is achieved by operating the unit at the inversion temperature of sound in water. The design features of the unit as well as water. The design features of the unit as well as the electrical characteristics of the system are discussed.