Enclosure for aircraft. Often used for maintenance. If armoured called shelter.
Ideal background for model photos. If you have no suitable poster available (remember the next airshow), it can be easily built. Normally the front part is sufficient. I made mine from a piece of styrofoam with a layer of cardboard where various pieces of polystyrene were glued onto and painted light gray. The "sky" background is light blue cardboard. See page "Modellfotos 3"
An absolute must for modelers (i.e. when discovering the one and only squadron badge decal was applied upside down).
Also to get wiser when in the services or being a pilot (or both). For very recommendable pages see:
A-4 Skyhawk.org humor page.