The Plunger class was an early class of United States Navy submarines, used primarily as training vessels for the newly formed "silent service" to familiarize navy personnel with the performance and operations of such craft. Most of these "A-class" submarines ended up being stationed in the Philippines, an American possession, prior to the outbreak of World War I. In some instances, this class of submarines is referred to as the Adder-class submarine, as USS Adder was the first boat of the class to be completed.