Final answer:
The first all-black regiment in the Union Army was the 54th Massachusetts Volunteer Infantry Regiment.
Step-by-step explanation:
The first all-black regiment in the Union Army was the 54th Massachusetts Volunteer Infantry Regiment. This regiment was formed in 1863 during the American Civil War. Led by white abolitionist officer Robert Gould Shaw, the 54th Massachusetts fought in the Battle of Fort Wagner and gained recognition for their bravery and valor.