Here's the whole ass list. I personally like how half the letters have some C-130 variant.
A: Attack (A-10, AH-64, AC-130)
B: Bomber (B-52)
C: Cargo (C-130, CH-47)
D: Drone director OR Delivery (Former isn't used anymore, latter is basically unmanned cargo, GD-2000)
E: Electronic warfare (EA-18G, EC-130)
F: Fighter (F-22)
G: Glider (GD-2000)
H: Search and rescue/medevac OR helicopter (HC-130, HH-60, AH-64)
K: Tanker (KC-130)
L: Modified for cold weather operations (LC-130)
M: Multi-mission (i.e., Special Operations) (MC-130, MH-60, MH-47)
O: Observation (OV-10, OA-1K)
P: Maritime patrol (P-3, P-8)
Q: Unmanned aerial vehicle (MQ-1, MQ-9)
R: Reconnaissance (RC-135, RC-130, RAH-66)
S: Anti-submarine warfare OR space plane (S-3, SH-60, latter isn't used yet just forward looking)
T: Trainer (T-38, T-7)
U: Utility (UH-1, UH-60)
V: VIP transport OR vertical/short takeoff/landing (VC-25, MV-22)
W: Weather (WC-130)
X: Experimental (X-15, X-37, XB-70)
Y: Prototype (YF-22, YF-23)
Z: Lighter than air (IE blimps and dirigibles)(MZ-3A)