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Nap-of-the-earth (abbreviated NOE) is very low-level type of flight course used to avoid detection and attack by an enemy when in a high-threat environment.
Geographical features are used as cover, exploiting valleys and folds in the ground by flying in them rather than over them to avoid 'skylining' to an enemy and to keep below radar cover. Other terms such as 'ground-hugging', 'terrain masking', or 'flying under the radar' are also used
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