Application of laser interferometry to measurements of projectile motion in guns has led to resolutions of < 5pm in displacement, < 0.01 m/s in velocity, and < 0.1 μsec in time. These resolutions far exceed those available from alternative techniques such as microwaves, optical light beams, accelerometers, high-speed photography, etc., and promise to give designers of projectiles and guns a more accurate tool with which to substantiate their calculations and to optimize their designs. This paper describes two types of interferometers and their application to the measure-ment of motion of projectiles launched by conventional weapons and by smooth bore laboratory guns. A displacement interferometer, developed at RARDE, was used to measure the effects of engraving of the projectile driving band on overall projectile motion. From these measurements, the time-dependent frictional forces arising from the engraving process were calculated, providing information both on the engraving process and on the interpreta-tion of the pressure-time measurements made in the gun chamber. Measurements made with the velocity interferometer, first developed at Sandia National Laboratories, Albuquerque, ex-amined both initial motion and total travel of projectiles in smooth-bore gas guns over a velocity range of < 40 m/s to > 4000 m/s, demonstrating the wide dynamic range of the in-strument. Initial applications of this interferometer were to check the accuracy of hydrocodes used to predict the performance of two-stage light gas guns. The paper describes the design of the interferometer systems, their capabilities and limitations, and summarizes several of the uses to which they may be put as high-resolution diagnostics for measurement of gun parameters.