Signalling Balloons
Using balloons of different colours at different heights is an effective way of signalling if you're not in a hurry, the sky is clear and the enemy doesn't shoot them down
Picture No
10115128
Media ID
47320120
Size
5237px x 3504px
(2.1MB)
Credit
Mary Evans Picture Library
Source
Unnamed artist in an unidentified encyclopedia
Date
Late 19th century
