4-27. The Army has increasingly emphasized externally supported training events in which a headquarters senior to the unit being trained provides assistance in the form of detailed planning, additional resources, and evaluation. Support provided by the higher headquarters usually includes a METL derived scenario with associated training and evaluation outlines (T&EO), an OPFOR, observer/controllers, and evaluation support. The Army's CTCs are prime examples of training opportunities that provide combined arms battle focused training that is externally supported. CTCs provide training events based on each participating organization's METL and conducted under realistic and stressful conditions. Externally supported training events can also be conducted at home station to enable units to focus exclusively on the execution of training.