http://www.rockislandauction.com/viewitem/aid/67/lid/261

Patented by John Walch in 1859, this is a .36 caliber revolver using superimposed chambers - meaning that each of the six chambers could hold two shots, for a total of 12 rounds before reloading. The revolver has two hammers and two side by side triggers, with the trigger for the front loading being positioned slightly ahead of the rear load's trigger, to help ensure that they are fired in the correct order.

While the 12-shot capacity was a major advantage over other revolvers of the period, number of significant disadvantages (weak charges because of the small chamber capacity and the safety hazards of a misfire or accidental firing of the rear load first) led to it being produced only in small numbers. About 200 of these .36 caliber Navy guns were made, and only for commercial sale. They did see use in the Civil War, though, as did most other guns in production at the time. A much more popular version was the 10-shot, .31 caliber pocket model.