The system conveyed its information in the form: For example, F4U-1A referred to a minor modification to the first major subtype of Chance-Vought's fourth fighter design. For the first few years after the system was introduced, the manufacturer's letter and the mission letter were sometimes reversed. If it was the manufacturer's first design for that particular mission, there was no number before the manufacturer letter.
Mission
The mission of the aircraft was designated by a one or two letter code. This code would also indicate whether the craft was a glider, helicopter or lighter-than-air. Duplicated codes were not in use at the same time.
Design number
In cases where an aircraft was its manufacturer's first design for a particular mission, the 1 would not be written. Thus the Consolidated Catalinapatrol aircraft was the PBY, not PB1Y, and the McDonnell Phantom was FH, not F1H.
Manufacturer
The codes used to denote manufacturers were not unique to a single company as they were reassigned, usually when the company had either ceased operations or had not produced an aircraft for the Navy for a considerable period of time. Additionally, aircraft built under license received a separate design number than the aircraft produced by the designing company. For example, Goodyear produced the Vought F4U Corsair as the FG and the Grumman TBF Avenger torpedo bomber was produced by General Motors as the TBM. Foreign aircraft generally did not receive a designation under this system unless they were to be built under license in the United States, or were built for use in the United States, such as aircraft built in Canada, including the Fairchild-Canada SBF Helldiver and Canadian-Vickers PBV Catalina.
Minor modifications
Letters were occasionally appended after the design number to denote minor modifications to the subtype; e.g. adding 'N' to the Grumman F6F-5 Hellcat designated the radar-equipped night fighter version of that model: F6F-5N. The first suffix to be used was "C" for aircraft modified for launching from an aircraft catapult on a battleship. Before World War II, the suffixes were often consecutive, with many lacking defined meanings, and they were not often used. During the war, they came into wide use and were given defined meanings, but these were confusing and inconsistent, with letters being duplicated. For instance, the letter "A" was used both for deletion of the tailhook from an aircraft normally so equipped and for addition of this equipment to a land-based aircraft; for amphibious versions of flying boats ; for armament added to a normally unarmed type; and for miscellaneous modifications. The addition of a tailhook to a land-based aircraft could also be designated with a "C", e.g. the North American SNJ-5C, repeating the letter previously used for catapult-launched aircraft. A significant wartime exception to this system was existing United States Army Air Forces types adopted by the Navy, such as the North American B-25 Mitchell; in some such cases, the minor modification letter simply mirrored the USAAF sub-type letter, e.g. the B-25H became the PBJ-1H.
A very similar system, the short system, was adopted by the Imperial Japanese Navy Air Service in the late 1920s that differed only in the use of the 1 for the first assigned type, having letters assigned to match Japanese aircraft and manufacturers, and not having a different number series for each manufacturer.
