Communicating with Planes: A Second World War Signal Book for Air Navigation

January 29, 2020

In February 1940 Britain was holding its breath. War against Germany had been declared the previous September, but no major military actions had occured on the Western front. Government and military preparations, however, were in high gear, and civilian rationing had been established just a month earlier. It was in this heightened atmosphere that this aviator's signal book was published by the United Kingdom's Air Ministry.

Designed for air crews and ground or ship-based workers who might encounter planes, the signal book was designed to facilitate communication using the International Code of Signals. The ICS had its origin in naval flag signalling, though it would come to include a number of techniques, and was first officially codified in 1920. Also incorporated are signals and procedures prescribed by the International Air Convention of 1919, the first attempt to simplify and standardise the patchwork of practices governing international aviation.

So what do these signals entail? The most obvious in a theatre of war is national identification, and the signal book includes eleven pages of flags and the way those flags are displayed on aircraft (see the photo at the top of this post). There are also explanations of navigation lights - the red, green and white lights that are still used today to indicate a plane's position and direction relative to an observer. For instance, if when looking at a plane the lights you see are red on your right and green on your left, the plane is moving directly toward you. If green is on your right and white on your left, the plane is moving away from you towards your right. There are also light arrays for barrage balloons!

Ground signalling for both day and night is another important aspect of aviation reflected in the guide. 

As are ground lights to indicate runways and obstructions.

Navigation and ground lights at airports will be familiar to many frequent fliers and plane enthusiasts, but I had been unaware that there was (is?) a signalling system designed for grounded planes to communicate with those flying above them. It utilises flat bands and discs — presumably these were fabric panels supplied as part of the standard kit for each military plane (or made from whatever was available at the time), but I've been unable to find any information about whether the system was regularly used in practice.

This system would have been very flexible, capable of relaying a large number of messages. Anything from "I require petrol/arms and ammunition/food supplies" to "All is well. I can carry out repairs and take-off without assistance"; "Landing will be possible at low tide"; and "I am proceeding in the direction indicated by the 'T', but I intend returning here".

My other favourite section is the long list of one, two, and three-letter morse signals. These were designed so that frequently used messages could be transmitted more quickly and easily than by sending whole sentences. For instance, in just two letters (AC) an aviator could report that "Aircraft will have to be abandoned" or "I am aground and require immediate assistance" (AT). 

The signal book gives hundreds of these codes, which could be used in communication with ships and ground workers, as well as other pilots. Some would have allowed aviators to report weather conditions and icebergs to ships: "I sighted an ice field" (OU); "Have you sighted any ice, if so , state position and whether berg or pack ice?" (PA).

Also of interest, is that this copy bears evidence of use. A former owner has made three small pages of neat notes about morse code procedure and loosely inserted them at the front of the book. The handwriting is the correct style for the period of the Second World War, so it seems like this was a indeed a working copy owned by a service member or perhaps a civilian worker at a government installation or airfield. It's certainly a wonderful record of aviation procedures of the period, and what the British Air Ministry considered important to include in a signal book at the outset of a war that would soon engulf much of the world.