The Plunger class was an early class of United States Navy submarines. In the first years of their service, they were used primarily as training and experimental vessels for the newly formed "silent service" to familiarize naval personnel with the performance and operations of such craft. They were known as the "A class" after being renamed to A-type designations (A-1 through A-7) on 17 November 1911. All except Plunger ended up being stationed in the Philippines, an American possession, prior to the outbreak of World War I. They were shipped there on colliers (coal-carrying ships) and formed an integral part of the harbor defense system for Manila. In some instances, this class of submarines is referred to as the Adder class, as USS Adder was the first boat of the class to be completed. Design and construction These boats were essentially an enlarged and improved version of the Holland, with a much more powerful 4-cylinder, 160 bhp Otto engine and an enlarged battery. Their increased size allowed a crewman to stand upright inside the boat. They were designed by Electric Boat under the direct supervision of John Philip Holland and were known to the company as design EB 7. The design was considered such an advance over the Holland that the company took the unusual step of ordering a prototype of the class using internal company funds. The prototype, named Fulton, was built at Lewis Nixon's Crescent Shipyard in New Jersey. It was a fortunate move, as the Fulton's company trials turned up numerous deficiencies that needed to be corrected. These trials, along with the need to correct the noted deficiencies delayed the building of the Plungers quite a bit. On average the boats were delivered to the Navy two years late. Although Fulton eventually did quite well on trials, proving the capabilities of the Plungers, there were no approved appropriations from the Navy to purchase her so she was sold to Russia, and renamed . A single hull design, all ballast and fuel tanks were located internally. The battery had 66 cells located underneath the torpedo reloads and was 24% more powerful than the one installed on Holland. The battery was open-topped, and when the decking was removed the battery acid could be seen sloshing around inside the cells. The top was shellacked wooden planks, with a layer of rubber above and finally a shellacked canvas covering. Holland's emphasis