"Many U.S. officials and Members of Congress view the United Kingdom (UK) as the United States' closest and most reliable ally. This perception stems from a combination of factors, including a sense of shared history, values, and culture, as well as extensive and long-established cooperation on a wide range of foreign policy and security issues. In the minds of many Americans, the UK's strong role in Iraq and Afghanistan during the past decade reinforced an impression of closeness and solidarity."
CRS Report for Congress, RL33105
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html