The arrangements vary according to the methods of training in the different Services. In the Royal Navy, the normal system of drafting instructors to sea at regular intervals will be observed. In the Army, National Service men and Regulars will train together in the same units; the latter will attend specialist courses as necessary. In the Royal Air Force, the duties required of the training staff are often in themselves sufficient to keep the men up-to-date, though flying instructors generally take a course at an operational conversion unit when leaving instructional work for operational duties.