This comes directly from the IRS:
Members of the military and certain other federal employees serving outside the U.S. have an extra year to buy a principal residence in the U.S. and qualify for the credit. Thus, an eligible taxpayer must buy, or enter into a binding contract to buy, a principal residence on or before April 30, 2011. If a binding contract is entered into by that date, the taxpayer has until June 30, 2011, to close on the purchase. Members of the uniformed services, members of the Foreign Service and employees of the intelligence community are eligible for this special rule. It applies to any individual (and, if married, the individual’s spouse) who serves on qualified official extended duty service outside of the United States for at least 90 days during the period beginning after Dec. 31, 2008, and ending before May 1, 2010.
This is a much deserved benefit given to military families. All that qualify should take advantage of the First time home buyer tax credit before it is no longer available.