Some of you might be wondering what the "K" stands for in my more recent constructions as of the day this was written. Here is what I aim to use to provide continuity to my aircraft designs of South Japan, the fictional nation who broke away from Japan proper:
Aircraft would be given designations depending on the military branch used. Prior to WWI, ALL aircraft were used by the Imperial Japanese Army, but the factories in South Japan had standardized the model designations, which in that reality inspired the Japanese Naval short designations.
Imperial Japanese Era(1910-1925):
A: Reconnaissance/Spotter
B: Spotter Destroyer(Fighter)
C:Scout Bomber(Antiquated by war's end, Dropped grenades)
D:Trench Attack Aircraft
E:Light Bomber
F:Medium Bomber
G:Heavy Bomber
H:Trainer
I:Heavy Fighter, Subdesignation
J:Torpedo Bomber
K:Transport
L:Night Fighter Subdesignation
Z:Prototype
X:Experiment

After 1925, South Japan was granted sovereignty, under the condition that medium and heavy bombers were retired and none operated with a payload greater than 2 tons.

Independent Designations:
A:Destroyer(Light fighter, made for high maneuverability, eventually a mix between speed and maneuverability, not necessarily long range)
B:Fighter(Designed for high speeds, most have higher fuel capacities than the destroyers, but are lighter than contemporary heavy fighters)
C:Reconnaissance Aircraft
D:Cruiser/Air Cruiser(Heavy Fighter, made for long range and heavy armaments, including a 20mm cannon or larger, aircraft that don't fit this role completely usually have this designation as a subdesignation)
E:Personell transport
F:Cargo Transport
G:Dignitary Transport
H:Light Ground Attack Aircraft(Can carry small bombs, with almost the same firepower as that of a heavy fighter)
I:Ground Attack(Very powerful guns and long range, but can't perform well enough to be a fighter in a standalone designation, a bomber version of a fighter as a sub-designation, typically carries up to 1000lbs of bombs)
J:Light Dive bomber, carries the same bomb load as a Ground Attack Aircraft
K:Light Bomber/Medium Dive Bomber/Heavy Ground Attack(Carries from 1500lbs of bombs to 2000lbs)
L:Tactical Bomber(Heaviest Army bomber, carries from 2500lbs of bombs to 3000lbs)
((Aircraft designed for the airforce under these designations that have reached prototyping stage would use these designations))
M:Medium Bomber
N:Strategic Bomber(4500-7500lbs of bombs)
O:Heavy Bomber(8000+lbs of bombs)
P:Escort Fighter Subdesignation

The air force official aircraft designation would use the K-###X# designation, the first set of pounds represented the year the aircraft was put into service since colonization(in 40 AD, or Japanese Imperial Year 700 for reference), followed by the designed role for the aircraft, followed by the mark of the plane. EG:
K-94Ba Designation would mean the aircraft was put into service in Colonization Year 1894(1934) as a bomber. K-99J1O would mean Col. year 1899 as a heavy fighter, though built as an escort fighter version of the Mk. 1 K-99J.