SSK was the United States Navy hull classification symbol for a diesel-electric submarine specialized for anti-submarine duties. SS indicated that the vessel was a submarine, and the K suffix that it was a hunter-killer. The United States Navy does not currently operate any submarines of this type, and so the designation is inactive. The only purpose-built ones were the three Barracuda-class: * USS Barracuda (SSK-1) * USS Bass (SSK-2) * USS Bonita (SSK-3)