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Small enclosures surrounded by a strong embankment on two or three sides but open from the front (and in some cases also from the rear to cater for jet efflux or to permit entry of aircraft) to admit and store aircraft. Blast pens are also designed for storing or parking missiles, specialist vehicles, etc. Also called a hardened shelter.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved