WordNet (r) 3.0 (2006):

task force
    n 1: a temporary military unit formed to accomplish a particular
         objective
    2: a semipermanent unit created to carry out a continuing task

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "task force":
   KP, Naval Construction Battalion, RN, Royal Navy, Seabees, USN,
   United States Navy, argosy, armada, army, army group, battalion,
   battery, battle group, brigade, cadre, coast guard, cohort, column,
   combat command, combat team, company, corps, detachment, detail,
   division, escadrille, field army, field train, file, fleet,
   flotilla, flying column, garrison, kitchen police, legion, maniple,
   marine, merchant fleet, merchant marine, merchant navy,
   mosquito fleet, naval forces, naval militia, naval reserve, navy,
   organization, outfit, phalanx, platoon, posse, rank, regiment,
   section, squad, squadron, tactical unit, task group, train, troop,
   unit, wing