Photo de stock - Oct. 10, 1969 - The Spy-in-the-sky helicopters employed to track down hijacked Lorries.: An operation was staged yesterday to demonstrate the efficiency of helicopters which have joined the Vehicle Obsever Corps, the voluntary organisation which watched for stolen lorries. Two helicopters are in the scheme at the moment, and later it is hoped that other private companies operating helicopters will join on a voluntary basis. The idea is that the pilots should report anything suspicious noted during their journeys. Hauliers are asked to paint a symbol, or some distinctive signs on the top of their lorries carrying loads worth thousands of pounds the main targets for the hijack gangs. The symbol or markings on the top of the lorry are spotted by the helicopter and the pilot contacts the police radio car which then chases after the stolen lorry. Hertfordshire police took part in yesterday's exercise at Welwyn Garden City, to demonstrate the effectiveness of the new helicopter technique. Photo shows a scene during the yesterday's exercises at Welwyn Garden City, Hertfordshire, showing a view from the helicopter as the police car stops the 'stolen' lorry with special markings after a report from the pilot. (Credit Image: © Keystone Press Agency/Keystone USA via ZUMAPRESS.com)