fieldwork

from WordNet (r) 3.0 (2006)

fieldwork
    n 1: a temporary fortification built by troops in the field

from The Collaborative International Dictionary of English v.0.48

Fieldwork \Field"work`\, n. (Mil.)
   Any temporary fortification thrown up by an army in the
   field; -- commonly in the plural.
   [1913 Webster]

         All works which do not come under the head of permanent
         fortification are called fieldworks.     --Wilhelm.
   [1913 Webster]