GPS compasses share the main advantages of gyrocompasses. Precession is also the mechanism behind gyrocompasses. There are certain circumstances when magnetic compasses and gyrocompasses are unreliable. These were (and remain) widely used for attitude indicators and gyrocompasses. Magnetometers, and substitutes such as gyrocompasses, are more stable in such situations. In addition, RCN vessels were incapable of operating gyrocompasses, making ASDIC attacks more difficult. Fluxgate compasses and gyrocompasses complement one another nicely. Gyrocompasses usually have built-in damping to prevent overshoot when re-calibrating from sudden movement.