When addressing an individual with an acting rank, the person should be addressed as if the full rank was held. For example, a member who is an acting master seaman would be addressed as "Master Seaman Smith", and not "Acting Master Seaman Smith" since the "acting" is a designation, regardless of the individual's actual rank and clerical designation. In writing, the acting nature of the rank may or may not be spelled out, so that the forms e.g. "acting captain", "captain (acting)" or "captain" may be seen. Documents dealing with rank, seniority and promotion will tend to spell out the acting nature of the rank, and informal documents will tend to avoid it, but no general rule can be said to exist for all contexts, nations or times.
In the United States Navy, acting appointments were common during the 19th century. The number of commissioned naval officers at each rank in the Navy was fixed by Congress, so it was difficult to fill vacancies if the number of officers needed to man ships exceeded that fixed number of officers allowed by Congress. Acting appointments were also common with warrant officers and ratings, although neither were subject to congressional approval and were simply temporary assignments.
The regulations stated that in the United States, acting appointments were not allowed unless specifically authorized by the Department of the Navy. In most other cases, only the commander-in-chief of a fleet or squadron would be authorized to appoint an officer to fill a vacancy, and this order would be subject to approval of the Department of the Navy. In this way, the Department of the Navy was able to fill vacancies while the Navy grew before Congress took action to permanently increase the number of officers. Outside of the United States and not part of a fleet or squadron, the commanding officer of the ship was allowed to appoint officers to a higher rank in the case of death on board the ship.
The officer was temporarily appointed to the higher rank, appended "acting" to his new rank, wore the uniform of the higher rank, and was addressed and paid at the higher rank. When the ship returned to the United States, or joined a fleet or squadron, the appointment was subject to review by the commander-in-chief of the fleet or squadron or the Department of the Navy.
Another type of temporary appointment was an "order to perform". This was issued in a similar manner to an acting appointment for a lower grade officer to perform the duties of a higher grade officer, except that their pay, rank and uniform remained at the lower grade.