The modern era of defending American harbors with controlled mines or submarine mines began in the post-Civil War period, and was a major part of US harbor defenses from circa 1900 to 1947.
A controlled mine (at left), with the distribution box that connected it and the other mines in its group to the mine casemate on shore.
This WW2-era mine, with its anchor, is on display at Fort Warren in Boston Harbor.
The mine casemate at Fort Strong, Long Island, Boston Harbor, once the control point for mines in the southern channels to the harbor.
A mine casemate had a control panel like this for each 19-mine group under its command. The controls were used to test and to fire the mines.