When they built the airport, the local farmers were outraged over the situation (seems the concept of eminent domain never has been understood by the Japanese). There were numerous terrorist attacks on the airport, and even recently there have been rocket-propelled grenades and missiles found near the outskirts...

Anyway, as a result you have to show ID no matter how you enter the airport (train, car, bus, etc.) as they are on the lookout for known terrorists -- especially the home-grown ones.

Note that KIX, NGO and other airports in Japan never had this problem, hence the ID formality does not exist elsewhere in Japan as far as I know. NRT is also unique in that take offs and landings can not occur after 11pm nor before 6am as I recall -- another concession given to the people of Narita in order to build the airport.

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