A NOTE ON SERIAL NUMBERS

US AIR FORCE / US ARMY

Origins
Serial numbers are the primary means of aircraft identification with the number allotted to an aircraft
remaining unchanged throughout it's service life, even if it becomes an instructional airframe.
In some cases however, if an aircraft goes through a major rebuild, new serial numbers are assigned,
several examples of this are the Douglas A-26A-OM Counter Invaders and the Boeing E-8 J-STARS
program. Inter-service transfers are another example of where serial numbers are changed as different
services have different systems.

The first US military aircraft was a Wright Model A, purchased on February 10th, 1908 and given the
serial number 1. Subsequent aircraft purchases were given the number 2, 3, 4 etc. Later these numbers
were prefixed by SC (Signal Corps.) in July 1914, AS (Air Service) in May 1920 and AC (Air Corps.)
in July 1926 which was continued up to 1941 when the USAAC became the USAAF.
Blocks of serial numbers were initially reserved for certain aircraft types - 200 for seaplanes, 40000
for experimental aircraft and 94000 for prototype and foreign purchases.

The Fiscal Year System
In 1920, after the Air Service was reintegrated with the US Army as the US Army Air Service it was
decided that future procurement of aircraft would be through the Fiscal Year (FY), with serial numbers
reflecting this. So, the first aircraft ordered in FY 1922 (July 1st, 1921 - June 30th, 1922) would be presented
as 22-1. The new system caused some confusion with aircraft still in service under the old AS system with
numbers in the 22000 and 23000 blocks. To avoid this and cases of duplication, many blocks in the FY 1922
to 1925 were left unassigned.
On July 2nd, 1926 the United States Army Air Corps. (USAAC) came into being and the Fiscal Year System
was retained and is still in use up to the present day for air force and army aircraft.
The Fiscal Year assigned to the serial number is the year in which the order was placed for the aircraft, not
necessarily the year in which it was completed. For example the XB-19 was ordered in FY 1938 but didn't
fly until June of Calendar Year 1941, the very end of FY 1941.

Presentation
Serial numbers were originally presented on aircraft
fuselages in small stenciled letters like so:
North American O-47A
A.C. 38-284

In 1941-1942 serials were introduced to the tails
of aircraft with the last digit of the FY year and
the full FY sequence number, so B-17G-35-DL
s/n: 42-107027 was presented as:
2107027
Fin serial numbers were never less than four digits,
the reason being that these were used as radio call signs.
So serials under the 100 mark had zeros added to fill them out.
So C-124C s/n: 53-1 was presented as:
3001
Longer serial numbers were also sometimes shortened to four
digits as in this example of F-86D-50-NA s/n: 52-10035
being presented as:
2035

Duplications and the Zero Prefix
In the early 1940's it was not expected that aircraft would last
longer then ten years in service so there was no need to deal with
serial number duplications.
The problem did arise in the 1950's and between 1956 and 1964, aircraft
over ten years old were prefixed by a 0 digit. This simply means the
aircraft has been in service longer than ten years, not obsolete
as many references will state.
Grumman SA-16B Albatross s/n: 51-7205
originally presented as:
17205
was now presented as:
0-17205
Longer serial numbers were also often shortened which
could mislead identification in some cases.
Douglas C-47A-70-DL s/n: 42-100785 was shortened to:
0-00785
Other cases saw the entire number with the
FY digit also included as in this example of a
Douglas SC-47A-75-DL s/n: 42-101000 presented as:
0-2101000
This system was discontinued in the mid 1960's with the
duplication of serial numbers every ten years considered
insufficient as long as the same serial number was not
applied to he same aircraft type.
When this situation arose the serial number block would be
"skipped"" over to the next block that did not clash with
the previous ten-year numbers.

The 1958 Extra Zero
In 1958 radio call signs were expanded to the use of five
digits with aircraft already in service under the 1000 mark having
an extra zero or zeros added to fill them out.
 So for FY 1958 the first aircraft was a Boeing KC-135A-BN
with s/n: 58-1 now presented as:
80001
Aircraft already in service had their serial numbers modified
to suit the new call signs.
For example Boeing B-52A s/n: 52-003 was originally
delivered with the tail marked as:
2003
was then modified to the 1958 extra zero call sign number:
20003
before finally given the over ten years old serial prefix as:
0-20003
A total of three serial number changes.

US Presidential Serial Numbers
One occasion where serial numbers are not allocated
in strict numerical order was on the two VC-137C and
VC-25A Presidential aircraft. "Air Force One" is the
correct radio call sign for when the President is
on board. These allocations were a special order
change to allow better distinction of the call signs
in situations where the President is not on board.
The first VC-137C was s/n: 62-6000:
26000
The second VC-137C was s/n: 72-7000:
27000
This allowed quicker identification between the two aircraft.
The two VC-25A's were ordered in FY 1986 and were
assigned s/n: 86-8800 and 86-8900.
A special order change was issued which saw these two numbers
changed to 82-8000 and 92-9000 respectively and
presented as:
28000
and
29000

Missile Serial Numbers
From FY 1958 to FY 1967 some Air Force missile and RPV orders were
procured with FY serial numbers usually in the 11000 / 13999 and
5000 / 19999 ranges.

Army Serial Number Changes
From FY 1967 to FY 1970 the US Army began a new series of
its own which saw the conventional use of the last digit of the
Fiscal Year but started the sequence numbers at 15000.
So, the first US Army order for FY 1970 was a Boeing-Vertol
CH-47C Chinook s/n: 70-15000 which was presented as:
015000
Quite often the year prefix was dropped and this lead to
a duplication problem on some aircraft.
From FY 1971 the serial sequence numbers have started at
20000 and continued consecutively since then without
reference to the Fiscal Year of purchase. 
For example the last Army aircraft ordered in FY 1976 was a
Bell AH-1S-BF Cobra s/n: 76-22713 and the very first aircraft
ordered in FY 1977 was a Sikorsky UH-60A Blackhawk
with s/n: 77-22714.

South-East Asia War
Increased procurements and security restrictions brought
about by the war in Vietnam saw from about 1969 onwards
the presentation of serial numbers on camouflaged tactical
aircraft changed so exact numbers built could not be determined.
Only the last three digits of the serial number were presented
in conjunction with a two letter unit code.

Buzz Numbers
At the end of World War II there was an abundance of well trained and confident pilots who
frequently flew low over air-bases or residential areas. In order to prevent this and possible
accidents the 8th Air Force in Germany introduced a letter / number code system for
quick identification of low flying aircraft on November 6th, 1945, termed after what they
were designed to stop - "buzzing" of airfields etc.
The first letter denoted the type - A (Attack), B (Bomber), generally the same as the Type
Letter in the designation system. The second letter has no meaning except for just being
the letter assigned to that aircraft variant. The numbers were simply the last three digits
of the serial number. For example cargo type C-82A-FA s/n: 45-57746 was assigned
buzz number CQ-746 with Q being the letter assigned to the C-82 model.
Where duplications occurred under the same two letter code, an A suffix was added, then
a B etc. for any more duplications that may follow.
For example:
F-84B-16-RE  s/n: 45-59558
assigned buzz number: FS-558-A
F-84B-21-RE  s/n: 46-558
assigned buzz number: FS-558-B
F-84C-11-RE  s/n: 47-1558
assigned buzz number: FS-558-C
Buzz Numbers were dropped in the mid 1960's when camouflaged aircraft began to appear
with low-visible serial numbers. The last use of Buzz Numbers was in 1971.

US NAVY / US MARINES

Serial numbers were given from the very beginning to all aircraft acquired for service by the
US Navy and US Marines under the following systems:

First Alphanumeric Series (1911-1914)
Not only the first serial number system but it was also the main designation system for naval
aircraft at this time with allocations having a single letter to denote manufacturer followed by
a number to indicate order of procurement. For example A was the designator for Curtiss
aircraft and four in total were delivered, hence serial numbers A-1 / A-4.
Second Alphanumeric Series (1914-1917)
The second system used was a two letter code that indicated both aircraft type and role.
This was again followed by numbers denoting order of procurement and like the first series it was
also the main designation system for naval aircraft under this series.
On February 10th, 1916, it was decided by the Department of the Navy to order the Office of Naval
Aeronautics to give every aircraft ordered a single assigned consecutive number which resulted
in the introduction of the next series.
First Bureau Number Series (1917-1935)
On May 19th, 1917, a new system was introduced starting at the number 51, (there were only
about this number of aircraft in the US Navy at the time), prefixed by the letter A (Aeroplane).
The previous system was gradually abandoned and serial numbers under the new system had
run up to A9204 by June 1930. The A prefix was then dropped and the numbers continued
from 9205 up to 9999 where in 1935, the series was revised.
Second Bureau Number Series (1935-1940)
The Bureau Number series was restarted at 0001 in 1935 and ran up to 7303 in 1940 when
the US Navy found with the imminent possibility of entry into World War II that serial numbers
would be duplicated with the massive aircraft orders being made to fight a war on two fronts.
It was then decided to again restart the numbering sequence.
Third Bureau Number Series (1940-present)
Starting with BuNo. 00001, a Curtiss SB2C-1 Helldiver, in 1940, this series would see the US Navy
through World War II, the Cold War, Vietnam and up to the present day with the current BuNo.'s
having climbed well past the 166000 mark.
These numbers have become popularly known as Bureau of Aeronautics Numbers - shortened to
BuNo. during World war II.

US COAST GUARD

The USCG was formed on January 28th, 1915 to protect US territorial waters and the first Coast
Guard aircraft was taken on charge in 1927. 
Four series of serial numbers have been used:

First Series (1927-1934)
A simple numeric numbering system with an optional CG prefix.
Second Series (1934-1936)
A three number code system covering four aircraft types - 100 (amphibians), 200 (flying boats),
300 (landplanes) and 400 (floatplanes), with procurement numbers denoted in the last two
digit spaces.
Third Series (1936-present)
From October 13th, 1936, three digit numbers were used prefixed by the letter V (heavier-than-air).
Earlier aircraft were renumbered and aircraft transferred from other services usually had the last
three digits of their serial numbers carried over with the V prefix attached.
The V prefixed was dropped on December 28th, 1945 and from January 1st, 1951, was replaced
by the digit 1 to create the four digit radio call sign requirement. When Air Force or Navy aircraft
were transferred to the USCG their serial numbers were quite often carried over using only the
last four digits.
Executive Series
Two digit numbers assigned to aircraft under USCG operations for VIP / staff transport.

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