I'm trying to determine how tail and wing numbers were assigned just prior to WW2.  For example, I've seen a depiction of a P-40CU numbered "54 8P" http://www.internetmodeler.com/2004/february/new-releases/ced32052p.jpg .  Obviously the 8P indicates 8th Pursuit Group; what I'm wondering is whether the "54" was an abbreviated serial number, or simply some kind of prewar buzz code?  If the latter, was there a certain range of numbers assigned to each of the squadrons in the group.
 
Thanks much, this is puzzling and for once I can't seem to find the answer on the web. 

The system you refer to is the Revised Designator System for aircraft instituted in May 1940.

The following designators (with examples in parenthesis) allocated by that system:
AB = Air Base Group (5AB 1 = 5th Air Base Group plane #1)
AD = Air Depot (FAD 1 = Fairfield Air Depot plane #1)
AO = Air Officer (2AO 1 = 2nd Corps Area Air Officer plane #1)
B = Bombardment Group (2B 1 = 2nd Bombardment Group plane #1)
C = Communications Squadron (1C 1 = 1st Communications Squadron plane #1)
ED = School Squadron (63ED 1 = 63rd School Squadron plane #1)
HQ = Headquarters Squadron, GHQ Air Force/Air Force Combat Command (HQ 1)
IM = Instructor, Miscellaneous (IM 1)
MD = Material Division (located at Wright Field) (MD 1)
M = Miscellaneous or Composite Group (example 4M 1 = 4th Composite Group plane #1)
NG = National Guard Observation (example 54NG 1 = 154th Observation Squadron, NG plane #1)
O = Observation Squadron, Regular Army (22O 1 = 22nd Observation Squadron plane #1)
OR = Organized Reserve (8OR 1 = 8th Corps Area Organized Reserve plane #1)
PH = Photographic (1PH 1 = 1st Photographic Squadron plane #1)
P = Pursuit Group (20P 1 = 20th Pursuit Group plane #1)
R = Reconnaissance Squadron (41R 1 = 41st Reconnaissance Squadron plane #1)
S = Staff Squadron (1S 1 = 1st Staff Squadron)
T = Transport Squadron (6T 1 = 6th Transport Squadron)
TS = Technical Supervisor (TS 1)
W = Hq Sq, Wing (2W 1 = Hq Sq, 2nd Bombardment Wing plane #1)
WO = Weather Observing Squadron

It was common for a three-squadron group to reserve the numbers 1-9 for aircraft assigned to Group Headquarters Squadron,  numbers 10-39 to the first squadron, numbers 40-69 to the second squadron, and numbers 70-99 to the third squadron.   The Squadron commander generally took the highest or lowest number in each block.
Example for the 8th Pursuit Group (Interceptor):
8P 1 thru 5 (5 planes) belong to the Headquarters Squadron, 8th Pursuit Group
8P 10 thru 34 (25 Planes) belong to the 33rd Pursuit Squadron, 8th Pursuit Group
8P 40 thru 64 (25 Planes) belong to the 35th Pursuit Squadron, 8th Pursuit Group
8P 70 thru 94 (25 Planes) belong to the 36th Pursuit Squadron, 8th Pursuit Group
The above amounts of planes are bases on Table of Organization stength, not what they really had on hand in 1941.
That is how to identify your plane as belonging to the 35th Pursuit Squadron, 8th Pursuit Group as the caption says.

Mark

I suspected that this would be the place to find a helpful expert - thanks very much!  That was what I needed to know for this project: