It covers the various types of ships that support the frontline combat vessels of the United States Navy.

The difference is that 'MC Type' refers to ships designed by the United States Maritime Commission aka MarCom, while 'MA Type' refers to ships designed or converted under MarCom's successor agency, the United States Maritime Administration or MarAd.

Prior to the creation of the auxiliary hull classification system, ships that performed such tasks had no symbol or code to identify them, only informal designations such as Fleet Collier No.

During World War I the Navy created the Section patrol (SP) and identification number (ID) system to register civilian vessels for naval acquisition.

Also during WWI a series of mass-produced ships were designed by the Emergency Fleet Corporation, but few were completed before the end of the war and even fewer became naval auxiliaries.

Until World War II the US auxiliary fleet was notable for being composed of non-standard ships which had been purchased ad-hoc.

[1] Also at this time the Navy began the construction of 4 large net layers (AN)s and 3 minelayers (CM)s to a different basic design, but changing requirements resulted in all but one minelayer being redesignated as transports (AP)s and then converted into Landing ships, vehicle (LSV)s.[A 1][2] During the naval build-up for World War II over 700 vessels of Maritime Commission (MarCom, later MarAd) standard designs were converted to US Navy auxiliaries,[A 2] as were a few Landing Ships Medium (LSM)s: During the Cold War over 100 United States Maritime Administration (MarAd) standard designs were converted to US Navy auxiliaries:[A 5] Modern auxiliaries have been designed to reduce operating costs by introducing scales of economies with larger ships and by reducing manning requirements (a trend begun in 1949 with the introduction of manning non-commissioned ships with civilian crews under the Military Sealift Command and its predecessors - such ships carry the 'T-' prefix on their hull symbols and the USNS prefix rather than USS; ships with MV or SS prefixes are under long-term charter with the Navy rather than under Navy ownership).

Banner-class Robert D. Conrad-class Eltanin-class: MC type C1-ME2-13a Melville-class Hayes-class Diver-class Gyre-class Thomas G. Thompson-class Kilo Moana-class Neil Armstrong-class Underwater acoustics collection vessels.

APR was the original hull symbol intended for the patrol craft escorts that were converted to rescue crews from ships attacked in convoys, but they were instead redesignated as PCERs.

Fulton-class Griffin-class: MC type C3 Ex-commercial ships Aegir-class: MC type C3-S-A2 Uncertain class Hunley-class Simon Lake-class L. Y. Spear-class Emory S. Land-class Lapwing-class Chanticleer-class Penguin-class Pigeon-class Sonoma-class Arapaho-class Bagaduce-class Cherokee-class Abnaki-class Sotoyomo-class Lapwing-class The first ten boats of the Sotoyomo-class were originally classed as Fleet Tugs (AT), as were ATA-146, ATA-166, and ATA-167.

[36] Wright-class Jason-class Langley-class Curtiss-class[37] Patoka-class Currituck class Tangier-class: MC type C3 Pocomoke-class Chandeleur-class Kenneth Whiting-class: MC type C3 [38] unknown class Ashland-class Wright-class: MA type C5-S-78 Clemson class[40] The Auxiliary aircraft escort vessels (AVG) were redesignated Auxiliary aircraft carriers (ACV) on 20 August 1942 and then Escort aircraft carriers (CVE) on 15 July 1943.