This image is taken from Training Manual TM 2160-20, "Submarine Mining," U.S. War Department, Washington, D.C., October 15, 1930, p. 217. It shows a spherical mine (cylindrical ones were also used) tethered to an anchor which kept it at a pre-determined height above the bottom. The mine is connected to a distribution box, a brass connection box weighing 300 lbs and providing protection for connections between the "shore cable" (running to the on-shore mine casemate) and the cables to the 19 mines that made up a mine Group. The buoys marking the mine and the distribution box were used during planting, and could also remain attached to the mines and equipment during service, at the discretion of the local commander. A typical distribution box had almost three miles of single-conductor cable running from it to the 19 individual mines of its Group.

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