[Betonov]

A Swedish Gotland sub sneaked inside a carrier group during exercises and took a photo of the USS Ronald Reagan and sneaked away.

Unfortunately I can only find a wiki article.

In 2004, the Swedish government received a request from the United States of America to lease HMS Gotland – Swedish-flagged, commanded and manned, for a duration of one year for use in anti-submarine warfare exercises. The Swedish government granted this request in October 2004, with both navies signing a memorandum of understanding on March 21, 2005.[5][6] The lease was extended for another 12 months in 2006.[7][8][9] In July 2007, HMS Gotland departed San Diego for Sweden.[10]
HMS Gotland managed to snap several pictures of the USS Ronald Reagan during a wargaming exercise in the Pacific Ocean, effectively "sinking" the aircraft carrier.[11] The exercise was conducted to evaluate the effectiveness of the US Fleet against diesel-electric submarines, which some have noted as severely lacking.

And

After being refit and upgraded to sustain the higher temperatures of tropical water,[4] HMS 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.[4]