vehicle carriers.

Captive register is a register of ships maintained by a territory,
possession, or colony primarily or exclusively for the use of ships
owned in the parent country; also referred to as an offshore register,
the offshore equivalent of an internal register. Ships on a captive
register will fly the same flag as the parent country, or a local
variant of it, but will be subject to the maritime laws and taxation
rules of the offshore territory. Although the nature of a captive
register makes it especially desirable for ships owned in the parent
country, just as in the internal register, the ships may also be owned
abroad. The captive register then acts as a flag of convenience
register, except that it is not the register of an independent state.

Flag of convenience register is a national register offering
registration to a merchant ship not owned in the flag state. The major
flags of convenience (FOC) attract ships to their registers by virtue
of low fees, low or nonexistent taxation of profits, and liberal
manning requirements. True FOC registers are characterized by having
relatively few of the registered ships actually owned in the flag
state. Thus, while virtually any flag can be used for ships under a
given set of circumstances, an FOC register is one where the majority
of the merchant fleet is owned abroad. It is also referred to as an
open register.

Flag state is the nation in which a ship is registered and which holds
legal jurisdiction over operation of the ship, whether at home or
abroad. Maritime legislation of the flag state determines how a ship
is crewed and taxed and whether a foreign-owned ship may be placed on
the register.

Internal register is a register of ships maintained as a subset of a
national register. Ships on the internal register fly the national
flag and have that nationality but are subject to a separate set of
maritime rules from those on the main national register. These
differences usually include lower taxation of profits, use of foreign
nationals as crew members, and, usually, ownership outside the flag
state (when it functions as an FOC register). The Norwegian
International Ship Register and Danish International Ship Register are
the most notable examples of an internal register. Both have been
instrumental in stemming flight from the national flag to flags of
convenience and in attracting foreign-owned ships to the Norwegian and
Danish flags.

Merchant ship is