Photos: U.S. Navy's submarine fleet The USS Michigan, an Ohio-class guided-missile submarine, arrives in Busan, South Korea, for a routine port visit in December 2010. Click through the gallery to see some of the other subs in the U.S. Navy's fleet. Hide Caption 1 of 8

Photos: U.S. Navy's submarine fleet A dolphin swims in front of the Virginia-class attack submarine USS John Warner during its sea trials in May 2015. Virginia-class subs, displacing 7,800 tons and at 377 feet long, "are designed to seek and destroy enemy submarines and surface ships; project power ashore with Tomahawk cruise missiles and special operation forces (SOF); carry out inntelligence, surveillance, and reconnaissance (ISR) missions; support battle group operations; and engage in mine warfare," according to the Navy. Hide Caption 2 of 8

Photos: U.S. Navy's submarine fleet The Ohio-class guided-missile submarine USS Georgia (SSGN 729) departs Naval Submarine Base Kings Bay to conduct routine operations in October 2015. Hide Caption 3 of 8

Photos: U.S. Navy's submarine fleet The USS Seawolf, shown here in support of European operations in June 2015, is the lead vessel in the three-boat Seawolf class. The Seawolf and the USS Connecticut, the second boat in the class, displace 9,138 tons and are 353 feet long. Click to the next slide to learn more about the third sub in the class, the USS Jimmy Carter. Hide Caption 4 of 8

Photos: U.S. Navy's submarine fleet The Seawolf-class attack submarine USS Jimmy Carter is moored in a Washington state facility that reduces a ship's electromagnetic signature in 2006. The Jimmy Carter is 100 feet longer than the first two subs in its class. The extra space is for a "multimission platform," the Navy says. "This hull section provides for additional payloads to accommodate advanced technology used to carry out classified research and development and for enhanced warfighting capabilities." Hide Caption 5 of 8

Photos: U.S. Navy's submarine fleet The U.S. Navy has more than a dozen ballistic missile submarines, also called boomers, in service. The boomers, 560 feet long, can carry 24 nuclear-armed Trident II ballistic missiles and serve as nuclear deterrents. Here, the Ohio-class ballistic-missile submarine USS West Virginia departs a naval shipyard in 2013. Hide Caption 6 of 8

Photos: U.S. Navy's submarine fleet The Ohio-class guided-missile submarine USS Ohio transits Puget Sound, Washington, in June 2015. The Ohio and three other guided-missile subs -- USS Florida, USS Michigan and USS Georgia -- were originally built and deployed as ballistic-missile subs, but were converted to guided-missile platforms beginning in 2002 after the Navy concluded it had a surplus of the boomers. Hide Caption 7 of 8