the higher temperatures of tropical water, HSwMS Halland took part in a multi-national exercise in the Mediterranean from September 16, 2000. Allegedly, there she remained undetected while still recording many of her friendly adversaries, attracting interest from the participating countries. In early November the same year, she participated in a NATO "blue-water" exercise in the Atlantic. There, she reportedly won a victory in a mock "duel" with Spanish naval units, and then the same in similar duel against a French SSN, a nuclear-powered attack submarine. She also "defeated" an American SSN, the USS Houston. Secondment to United States Navy In 2004, the Swedish government received a request from the United States to lease HSwMS Gotland – Swedish-flagged, commanded and manned, for a duration of one year for use in antisubmarine warfare exercises. The Swedish government granted this request in October 2004, with both navies signing a memorandum of understanding on 21 March 2005. The lease was extended for another 12 months in 2006. In July 2007, HSwMS Gotland departed San Diego for Sweden. In 2005, HSwMS Gotland managed to snap several pictures of during a wargaming exercise in the Pacific Ocean, demonstrating that it was in a position to sink the aircraft carrier. The exercise was conducted to evaluate the effectiveness of the US fleet against diesel-electric submarines, which some have noted as severely lacking. In 2001, during the exercise JTFEX 01-2 in the Caribbean Sea, the German U24 of the conventional 206 diesel-electric class "sank" the carrier Enterprise by firing flares and taking a photograph through its periscope. Overhaul Initial discussions In March 2013, Kockums received an initial order for an overhaul for two of the Gotland-class submarines. The overhaul was expected to be completed by 2017. With these upgrades, the submarines would be able to remain in active duty until after 2025. On 2 April 2014, the Swedish defence minister, insisting on the importance of submarines to the security of Sweden, announced the Government's intent to upgrade two of the Gotland-class vessels, as well as purchase two new "stealth" submarines of another type. Mid-life upgrade contract Negotiations concluded on 30 June 2015 with the signature of a contract between Sweden's Defense Material Administration (FMV) and Saab Kockums. In addition to the construction of two new Type 26 A SSKs, the contract provides for a mid-life upgrade of HSwMS Gotland and her sister ship HSwMS Uppland, for SEK 2.1