You sometimes come across the letter codes used by the artillery when communicating between units or with the aircraft of the Royal Flying Corps or Royal Air Force that flew observations missions to co-ordinate artillery fire. These codes are not always easy to interpret. This list comes from the private papers of 45222 Wireless Operator A. R. Atkinson RAF, held at the Imperial War Museum as document 89/12/1.

AR Air
AA Anti aircraft guns
RUF Are you firing?
B Are you receiving my signals?
CI Am returning to landing ground
KQ Are you ready to fire?
ART Artillery
BF Battery fire
CAV Cavalry
X Change to
COL Column
GO Go on firing in your own time
G Fire
GF Fire for effect (fleeting opportunity signal)
LL All available batteries to open fire (sudden or very favourable target)
XX Practice LL call
T General answer (or RD)
N Guns in position at
NF Guns now firing in position at
MM Trench mortars now firing in position at
NT Guns not firing at
GZ Graze
L High Explosive
FAN Infantry
MT Mechanical transport
Ht Horse Transport
M Mostly (as in mostly graze) or Mean point of impact
QM More left
KKH Sound ranging section standby
P Percussion
W Short unobserved or washout
VO Salvo
A Standby
MQ Stop firing or wait
SW Switch
EA Enemy aircraft
TNK Tanks
Ok Range (target)
Z Smoke shell
O Over
S Short
R Right
KB Continue firing with balloon observation
Q Left
RR More right
QQ More left
J Just
F ?
SC Smoke cloud obscuring target
ASF Sent when battery is firing for effect and observer wishes to range the guns afresh
SOS Barrage fire
WPNF Many batteries in square active (followed by location of square)
Weather codes
NBG No good for anything
DUD ditto
NGR No good for registration
NGP No good for photography
OK Fit
VIS Visibility
UL Unfit for counterbattery work
FL Fit for ditto
UE Unfit for registration
FR Fit for ditto
UD Unfit for photography
FD Fit for ditto
C Clouds
40 4000 (feet height of clouds)
Up Unfit for patrol
FP Fit for ditto
Links
Royal Artillery
How the British artillery developed and became a war-winning factor in 1914-1918