 Complete the following phrase:  Since 1987, the Pakistan Navy had been interested in acquiring the Type 21 frigates from the United Kingdom, and the Navy turned to the Royal Navy for an immediate purchase which was approved in 1993 whose expensive refitting and technological upgrades had to carried out by Pakistan itself at their Naval Base in Karachi over the years. In 1994, the Pakistan Navy entered in lengthy, complicated, and controversial negotiation with France to acquire the long-range submarine technology by dismissing the idea of procuring nuclear-powered submarine from China due to noise issue that the Indian Navy was quiet able to track. Despite embargo, the United States Navy maintained its relations with Pakistan Navy, inviting the Pakistanis to participate in the Inspired Siren in 1994, and gave the Pakistan Navy instructions and run down on the nuclear submarine and aircraft carrier operations. In an attempt to warm the political relations with the United States, the Pakistani military joined the 