The fourth grade of the specialist rank in the American Army was formerly indicated by the rank of SP4. The title was dropped in favour of “SPC,” the sole specialist level that roughly corresponds to corporal.
In order to give enlisted personnel with in-depth technical skills a comprehensive career path, the nine specialist ranks were added to the U.S. Army in 1955 and 1958. Armed Forces personnel with this kind of knowledge were probably used in technical capacities over the course of their military careers, making them too specialised to rise through the conventional ranks of troop leadership. For career service, the SP ranks offered status and financial benefits. Over time, SP levels were eliminated and reclassified as “SPC” ranks.