The armed forces' primary concern at this time, according to the ''National Defense Report'', is the possibility of an invasion by the PRC, consisting of a naval blockade, airborne assault or missile bombardment. Four upgraded ''Kidd''-class destroyers were purchased from the United States, and commissioned into the Republic of China Navy in 2005–2006, significantly upgrading Taiwan's protection from aerial attack and submarine hunting abilities. The Ministry of National Defense planned to purchase diesel-powered submarines and Patriot anti-missile batteries from the United States, but its budget has been stalled repeatedly by the opposition-Pan-Blue Coalition controlled legislature. The military package was stalled from 2001 to 2007 where it was finally passed through the legislature and the US responded on 3 October 2008, with a $6.5 billion arms package including PAC III Anti-Air systems, AH-64D Apache Attack helicopters and other arms and parts. A significant amount of military hardware has been bought from the United States, and, , continues to be legally guaranteed by the Taiwan Relations Act. In the past, France and the Netherlands have also sold military weapons and hardware to the ROC, but they almost entirely stopped in the 1990s under pressure of the PRC.