Three of the 100+ Union regiments and other units that trained or were housed on Hart and Rikers Islands at various times during the Civil War were USCTs: the 20th, 26th, & the 31st. Rikers’ 20th showed bravery in Battle for Port Hudson, La.  Rikers’ 26th saw fierce action in S.C. Hart Island’s 31st helped cut off the retreat by Gen. Lee’s forces at Appomattox, ending the war.
The Hart Island photo is a NYC Dept. of Correction (NYC DOC) photo in the archives managed by the NY Correction History Society. All rights retained by and reserved to NYC DOC. The Rikers Island pre-landfill image is based on a detail from an 19th century marine navigation map.