WASHINGTON (AFP) - General Martin Dempsey, who Friday took over as the US militarys top officer, has led soldiers in combat in Iraq and is keenly aware of the growing strain on the force after years of war. An Irish-American who taught English literature to cadets at West Point, the 59-year-old graduated from the same class at the military academy as another four-star general, David Petraeus. Until now, Petraeus who rose to fame as commander in Iraq and had stepped down as chief in Afghanistan to take over the CIA had largely overshadowed his former classmate. As commander of the 1st Armored Division in Iraq in 2003-2004, Dempsey oversaw tanks and troops that fought insurgents led by Shiite cleric Moqtada al-Sadr, pushing the militia out of southern cities. In his new job as chairman of the Joint Chiefs of Staff, Dempseys two combat tours will help shape how he advises the president as the United States wraps up its mission in Iraq and begins to withdraw some of the 100,000 American troops in Afghanistan. One of things hell bring to the job is current experience in the wars that were in, said David Barno, a retired lieutenant general and senior adviser at the Center for a New American Security. Dempsey takes over as chairman at a time of turmoil in the Arab world and growing pressure on the defence budget, with the Pentagon bracing for cuts and a possible scaled-back force. Unlike the outgoing chairman Admiral Mike Mullen, Dempsey is an extrovert with an irreverent sense of humor and a penchant for singing in public. Proud of his working-class roots in New York and New Jersey, Dempseys favorite tune is Frank Sinatras rendition of New York, New York, which he belts out with gusto in unabashed performances captured on YouTube.