Per Ardua ad Astra – ‘Through Adversity to the Stars’, The Latin motto of the RAF

Abbreviations
KIA – Killed In Action
MIA – Missing In Action
WIA – Wounded in Action
POW – Prisoner Of War

Abbreviations found in National Archives file AIR 2/6876 [*]
u/t – under training
AOS – Air Observer School
ATS – Air Training Scheme
BGS – Bombing and Gunnery School
EFTS – Elementary Flying Training School
GRS – General Reconaissance School
ITS – Initial Training School
OTU – Operational Training Unit
SFTS – Service Flying Training School
WS – Wireless School
PD or PDC – Pilot Disposal Center
PRC or RC – Personnel Reception Center
ACH/GD – Air Craft Hand/General Duties

More abbreviatons and acronyms on Words of WW2 and RAF abbreviations

Ranks
AM – Air Marshall
AVM – Air Vice Marshall
AC – Air Commodore (Modern RAF)
G/C – Group Captain
W/C – Wing Commander
S/L – Squadron Leader
F/L – Flight Lieutenant
F/O – Flying Officer
W/O – Warrant Officer
P/O – Pilot Officer
F/S – (Flight) Sergeant

Decorations
CBE – Commander in The Most Excellent Order of the British Empire
OBE – Officer in The Most Excellent Order of the British Empire
BEM – British Empire Medal
MBE – Member of The Most Excellent Order of the British Empire
DCM- Distinguished Conduct Medal
DFC – Distinguished Flying Cross
DFM – Distinguished Flying Medal
DSO – Distinguished Service Order
AFM - Air Force Medal

Sources
AD – Audrey Dewjee
AE – Audrey Elcombe
CG – Cy Grant, A Member of the RAF of Indeterminable Race, War Memoir
CMHA – Chuagaramas Military History & Aerospace Museum, Trinidad
CWGC – Commonwealth War Graves Commission
MOD – Ministry of Defence
NA – National Archives [*]
TDA – The Daily Argosy, Guyana (courtesy Mr. J.A. Lee, CMHA)
UC – Ulric Cross

[*] the file AIR 2/6876 gives a list of 298 British West Indians (including 50 officers) who attested in Canada for training as aircrew, and a nominal roll of 340 personnel (including 47 officers) from the Empire including the Caribbean (courtesy Guy Grannum, NA)