The Cairo is the sole survivor of the fleet of river gunboats built by the Union during the Civil War with the object of controlling the lower Mississippi River. Designed by Samuel Pook and built by James B. Eads, it saw limited battle and was sunk on the Yazoo River in 1862 by newly developed electronically detonated mines, becoming the first craft ever sunk by this predecessor to torpedo technology. The 175-foot ironclad vessel had 13 guns.
The USS Albacore (AGSS-569) represented a radical change in submarine design. The hull was designed with underwater speed as the prime requirement, and it was built with newly developed high-strength steel (HY-80). In addition to these two major innovations, the Albacore served as a test vessel for many new designs in submarine technology so that they could be refined before implementing them into the fleet. Among them was the testing of various control designs and correlation of actual sea-trial performance with that predicted in tow-tank tests.