Afghan Air Force Mi-24s in the hands of the ascendant Taliban gradually became inoperable, but a few flown by the Northern Alliance, which had Russian assistance and access to spares, remained operational up to the US invasion of Afghanistan in late 2001. In 2008, the Afghan Air Force took delivery of six refurbished Mi-35 helicopters, purchased from the Czech Republic. The Afghan pilots were trained by India and began live firing exercises in May 2009 in order to escort Mi-17 transport helicopters on operations in restive parts of the country.