The present disclosure relates to an electromagnetic actuator. The actuator comprises a casing, a sleeve, coils, a permanent magnet, cores and a movable plunger. The present disclosure is unusual in that the sleeve is made of magnetic material. The sleeve enables a single component to mechanically and hydraulically isolate the plunger from the coils. The sleeve is also made of a material having a lower saturation induction than that of the materials used in other parts of the magnetic circuit. The actuator is also suitable for incorporation into a submerged cryogenic valve.