Abstract: An apparatus for transmitting data from the exterior of a gun tube to a projectile positioned within the gun tube utilizes at least two electromagnetic-acoustic transduction devices, one such device positioned on or near the exterior periphery of the gun tube and one such device positioned on or near the interior periphery of the gun tube within the bore. Such data may be used to update target or trajectory information used by a projectile. Transmission of such data, at high data rates, just prior to firing the projectile from the gun tube, enhances the probabiity of target kill or damage. High data rates, compatible with SMART projectile requirements, are made possible by ultrasonic signal frequencies in the range of about 500 Khz to about 2,500 Khz. Phase-shift-keyed modulation may be employed to impart data onto the ultrasonic signals.