Austin headed U.S. Central Command, in charge of all U.S. forces in the Middle East and Afghanistan, between 2013 and 2016. He was the principal military architect of the U.S.-led international campaign to oust the Islamic State (ISIS), after the militant group seized swathes of territory in Syria and Iraq for its self-proclaimed ‘caliphate’, in June 2014.

A war plan drafted by Austin and his aides envisioned the U.S. military directly providing arms and training to Syrian opposition forces fighting ISIS on the ground and an increased air campaign by the U.S.-led coalition, based out of the Incirlik air base in Turkey.

The measures were intended to empower 3,000 to 5,000 Syrian Arab fighters who would join more than 20,000 Kurdish combatants in an offensive backed by coalition warplanes to push back ISIS.

Austin played a key role in organizing coalition airstrikes to repel ISIS attacks on the Kurdish town of Kobani in October 2014, according to the BBC. The ISIS siege on Kobani ignited mass protests in Turkey's majority-Kurdish southeast against the Turkish government’s lack of support, which led to deadly clashes with Turkish security forces that killed at least 37.

Austin said at the time that hundreds of ISIS militants had been killed as a result of the coalition's air operations, helping the Syrian Kurds reclaim territory they had lost.

At a congressional hearing in September 2015, Austin became the first military official to acknowledge the United States’ support for the People’s Protection Unit (YPG), a Kurdish-majority militia in Syria that Turkey views as an offshoot of the outlawed Kurdistan Workers’ Party (PKK).

U.S. Special Operations Forces are "engaged with the YPG", Austin said at the time, according to NBC News. U.S. Central Command later clarified that Special Forces were working with Kurdish forces in northern Iraq.

Defense officials said the commandos were operating in an "advise and assist role" and were not engaged in combat operations", being positioned far from the actual battle lines, according to NBC.

While answering questions before the Senate Armed Services Committee, Austin also revealed that a $500-million "train-and-equip program" to bolster Syrian opposition forces against ISIS went nowhere, saying that there were only four or five fighters left from the first group of 54 trained in the program at the time.

Biden’s decision to select Austin as defense secretary comes two weeks after he announced other senior members of his national security team. Austin’s appointment could be confirmed as early as Tuesday, people familiar with the plans told Politico.

Biden chose Austin because he is crisis-tested and respected across the military, one source said. Biden also trusts Austin, as they worked together when Biden was vice president in the Obama administration and had a large foreign policy portfolio, Politico said.

Austin, 67, is known as a battlefield commander, having served as vice-chief of staff of the army and the last commanding general of the U.S. forces in Iraq during the Obama administration’s troop pull-out from the country in 2011. Biden led Iraq policy during this time, Politico said.

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