A joint numbering system was introduced by the Army, Navy and Central Flying School in 1912.
Serials ran numerically from 1 upwards, with batches allocated to the different branches of the services as follows:
| 1-200 | Navy | ||
| 201-800 | Army | ||
| 801-1600 | Navy | ||
| 1601-3000 | Army | ||
| 3001-4000 | Navy | ||
| 4001-8000 | Army | ||
| 8001-10000 | Navy |
The Army further subdivided their initial allocation between different units:
| 201-250 | No.2 squadron | ||
| 251-300 | No.3 squadron | ||
| 301-350 | No.4 squadron | ||
| 351-400 | No.5 squadron | ||
| 401-600 | Central Flying School | ||
| 601-800 | Royal Aircraft Factory |
If an aircraft was transferred between a squadron and the CFS, Royal Aircraft Factory or Navy it would be renumbered, and if the original serial had not been applied to the aircraft prior to transfer the number would be re-used. A serial would not be re-used if an aircraft was simply written off.
Consequently serials in this range were not issued in sequence, and the system caused some confusion.
As a result this practice was discontinued in mid 1914, although the squadrons had abandoned the system much earlier.
Once 10000 was reached it was initially decided to continue the numerical sequence. However, it was recognised that the alternate allocation between services was causing confusion and the Navy were using their allocation at a much slower rate.
Consequently it was decided to prefix Army aeroplanes with the letter 'A' for Army and Naval aeroplanes with 'N' for Navy.
Army serials thus continued with the batch A1 to A9999 and Navy serials were issued in the range N1 to N9999
The Army had utilised the 'A' batch by late 1916 and continued alphabetically with B1 to B9999. The prefix letter 'G' was reserved for captured German aeroplanes and 'I' was not used. Within the 'C' range the batch C1 to C2000 was duplicated with aircraft used for training in Canada.
The last order placed before the end of the war was for the batch J6523 to J6572.
RFC Serials were initially allocated to individual aircraft when the machine was allotted to a unit following delivery and acceptance at Farnborough.
In early 1914 it was decided to change this system and allocate serials at the time the order was placed. This new system applied for serials in the range 502-599 and 748 upwards, gaps being left for the undelivered aircraft still on order.
The Royal Aircraft Factory rarely applied serials to aircraft produced by them, simply painting the aircraft type on the tail. The only known exceptions being:
| 601 | BE2 | ||
| 602 | BE2c | ||
| 604 | FE2 | ||
| 605 | FE3 | ||
| 607 | RE1 | ||
| 608 | RE1 | ||
| 609 | SE2 |
The 600 sequence was also utilised for aircraft hurriedly pressed into service in August 1914 upon the outbreak of war. The serial 608 was erroneously issued to a Bleriot impressed from the Bleriot School at Brooklands, ignoring the fact that the serial was currently in use by a RE1. As a result the Bleriot was re-numbered 605, the FE3 which originally bore this serial being no longer in use. The number 604 was similarly re-used by a Sopwith Tabloid.
Engines all had a manufactures serial number ('MN') and were also given a military number, generally running in numerical sequence for each engine type. This latter number was initially referred to as the 'AF' or Aircraft Factory number, and subsequently as the 'WD' or War Department number.
The engine number would generally be shown in reports as '22972WD1010' or '22972/1010' although in some case only one of the numbers would be shown. Of course it must be remembered that early engines were relatively unreliable and were frequently changed.