The inactivation of the last Armored Brigade Combat Team to be permanently based overseas leaves Washington’s foreign deployments reliant on US-based rotational forces, with implications for the US Army.

Personnel and tanks of the US 4th Infantry Division, deployed in Romania. Credit: DANIEL MIHAILESCU/AFP/Getty Images

By Henry Boyd, Research Associate for Defence and Military Analysis

The deterrent power of the United States Army’s heavy Armored Brigade Combat Teams (ABCTs) continue to underpin regional stability in Europe, the Middle East and on the Korean Peninsula. However, following the 2015 inactivation of the last ABCT to be permanently based overseas, all three of these tasks are now being filled by units on nine-month rotational deployment from the US, putting a significant strain on the army’s force-generation capabilities.

Going into 2012, the army had 17 armoured brigades in the active force. By the end of 2015 this number had dropped to nine as the army attempted to simultaneously adapt to both changing strategic circumstances and budgetary pressures. This headline figure overstates the actual force reduction, since the remaining armoured brigades all increased their assigned manoeuvre battalions from two to three as part of this process. Nevertheless, the drop from 36 manoeuvre battalions to 27 was still a significant decrease in available heavy combat power.

In addition, the inactivation of the last three armoured brigades based outside of the continental US (the 170th and 172nd Infantry Brigades in Germany and the 1st ABCT, 2nd Infantry Division in South Korea) now requires the army to meet the demand for heavy armour from commanders in Europe and Korea, as well as a continuing requirement in Kuwait, by rotating forces into theatre from the US for fixed tours.

The US Army force-generation process aims to achieve a dwell-to-deployment ratio of approximately two-to-one in the active force; i.e. a unit should spend two months at its home station resetting and training between deployments for every month it has been deployed. Continuously maintaining three simultaneous ‘heel-to-toe’ ABCT rotational deployments with this ratio in place therefore requires the use of all nine of the current active force ABCTs (see table).Table showing US Armored Brigade Combat Team deployments

Having all of its armoured brigades already committed leaves the army with little flexibility to meet potential contingency operations; any new allocation of heavy armour would require damaging changes in the dwell-to-deployment ratio. In theory, a resource that could be used to ease this burden on the regular army are the five Army National Guard ABCTs, but there remain significant cost and training obstacles to effectively employing this option. As a result, as the National Commission on the Future of the Army noted in 2016, in recent years the army has preferred to break its dwell-to-deployment ratio guidelines for active units rather than calling upon available reserve-component units.

One result of this has been a decision by the army to reverse the recent trend of cuts in ABCT numbers, and announce plans to add at least one, and ideally two, more armoured brigades to the active force by converting existing infantry formations. The first formation to convert – 2nd Brigade, 3rd Infantry Division at Fort Stewart in Georgia – is scheduled to begin receiving its new equipment in summer 2017, before its formal conversion to an ABCT later in the year. It should become available for deployment sometime in 2018.

This analysis originally featured on the Military Balance+, the new IISS online database that enables users in government, the armed forces and the private sector, as well as academia and the media, to make faster and better-informed decisions. The Military Balance+ allows users to customise, view, compare and download data instantly, anywhere, anytime.

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