LONDON (AP) -- London should not be turned into a "city under siege" by the heavy security measures being put in place for the Olympics, London organizing chief Sebastian Coe said yesterday. Coe spoke as the British military embarked on operations to test Olympic security, including flights over London by fighter jets and helicopters. Visitors to the Olympic Park encountered lengthy delays at times Wednesday as they went through airport-style security checks. "We want to make sure these games are safe and secure but at the same time we are not presenting a vision of London that is a city under siege," Coe said inside the Olympic Stadium. About 75,000 spectators are expected at Olympic Park on Saturday for five test events ahead of the July 27-August 12 games. Typhoon fighter jets from around Britain arrived Wednesday at a Royal Air Force base at Northolt in west London for the test operation, code named Exercise Olympic Guardian. It is the first time that fighter aircraft have been stationed at RAF Northolt since World War II. The Royal Air Force is also sending Puma transport helicopters and Lynx helicopters carrying teams of snipers trained to intercept aircraft flying without authorization in London's airspace. Olympic visitors could also encounter delays just getting into Britain, with a growing furore over recent snaking lines and lengthy delays at Heathrow Airport's immigration desks. "I'm actually confident that by the time we get to the games these are issues that will be behind us," Coe said.