A fleet formed in several short columns could change its heading faster than one formed in a single long column. Since most command signals were made with flags or signal lamps between ships, the flagship was usually placed at the head of the centre column so that its signals might be more easily seen by the many ships of the formation. Wireless telegraphy was in use, though security (radio direction finding), encryption, and the limitation of the radio sets made their extensive use more problematic. Command and control of such huge fleets remained difficult.