Rains graduated from the United States Military Academy at West Point, New York, in 1827, 13th in his class.

Rains, who turned 59 a few days after the battle, was one of the oldest officers in the Confederate army, and it was decided to reassign him to a less physically demanding job.

[1] The development of the first modern mechanically fused high explosive anti-personnel land mines was attributed to Rains during the Battle of Yorktown in 1862.

[2][3] (As a Captain, Rains had earlier employed explosive booby traps during the Seminole Wars in Florida in 1840.

Many of these designs were improvised in the field, especially from explosive shells, but by the end of the Civil War, nearly 2,000 standard pattern "Rains mines" had been deployed.