Union Iron Works, located in San Francisco, California, on the southeast waterfront, was a central business within the large industrial zone of Potrero Point, for four decades at the end of the nineteenth and beginning of the twentieth centuries.

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 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 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.