The basic TOE unit of the engineer system is the battalion. Although engineer battalions normally have a fixed organization, they may also be tailored for specific requirements. Battalions are employed when it is desirable to assign a unit with the complete control of a task or an area. There are four basic types of engineer battalions, plus a variety of different types of separate companies:
Combat Engineer Battalion (Divisional) -- Under provisions of the Engineer Restructure Initiative (ERI), each heavy division has an Engineer Brigade with three organic divisional engineer battalions organized and equipped to provide combat engineer support. These battalions will support the ground maneuver brigades of armor and/or mechanized infantry and consist of four engineer companies. The other divisions will have only one organic engineer battalion composed of four or five engineer companies. Regardless of structure, these battalions perform the primary combat engineer missions in the division's sector and forward.
Combat Engineer Battalion (Corps) -- Corps combat engineer battalions are normally assigned to a corps' engineer brigade (i.e. V Corps in Europe contains the 130th Engineer Brigade consisting of three engineer battalions and a number of separate companies). Most corps combat engineer battalions in Europe have been converted into tracked units (i.e. squads are transported in armored personnel carriers). Somewhat larger than the divisional engineer battalions, the corps combat engineer battalions provide combat and sustainment engineering support in the corps and division sectors. They may reinforce divisional engineer battalions and execute infantry combat missions when required.
Engineer Battalion (Combat Heavy) -- The combat heavy engineer battalion is normally assigned to an engineer brigade within a corps or theater army. The combat heavy engineer battalion has equipment and personnel skilled in earthmoving and construction. The battalion primarily works in rear areas on sustainment engineering tasks. However, its earthmoving capabilities may be effectively used to provide combat support in forward areas when not under direct fire (i.e. tank ditches, etc.). Missions include the construction of roads, airfields, structures and utilities for the Army and Air Force.
Engineer Topographic Battalion -- Engineer topographic battalions are assigned to the senior engineer headquarters of a theater army. These units provide topographic engineer and terrain analysis support to all units. It does not have the capability to accomplish infantry combat missions.