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, manning of foreign nationals, and, typically, 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.