Periodic amendments were made to the Field Service Pocket Book, a kind of military manual typically carried by officers. This one concerned the proper use of radios in the field.
Great Britain, War Office, Field Service Pocket Book, Pamphlet No. 2 – Amendments (No. 2) - Signal Security (July 1941) [Canadian edition, 1941])
War, Memory and Popular Culture Archives - The University of Western Ontario - London, Ontario
View PDF:FSP Signals.pdf
leaflet, 6 pages, 10.5cm x 16.2cm