Soldiers transport large balloon across a field.
French army observation post in tall tree.
American soldiers demonstrate search light on crane.
Soldier with rifle and Alsatian on guard...
Lord Thomson leaves by plane to conduct survey of Northern Rhodesia, Heston,...
Soldier Lifted by Kites an new surveillance method.
Photographic surveillance in the First World War.
Men pump up large observation balloon in field and launch it.
New periscope used for land surveillance.