Top views and longitudinal section of an American design for an impenetrable (impregnable) floating battery dated October 1861

National Archives/ Record Group 19: Records of the Bureau of Ships. Series: Ship Design and Construction Drawings

Of C. Gordon and J. Ericcson. 

Dimensions upper vessel 172 x 44.x 5 (depth) feet.

Dimensions lower vessel 124 x 34 x 6 (depth) feet.