"Dolphin" was originally built as a dispatch vessel, intended to courier messages as radio had not yet been invented. She was the only US naval vessel ever specifically designated as such. She was also called an "unarmored" or "unprotected" cruiser, and was eventually designated as a patrol gunboat (PG-24) on 1 July 1921, a few months before she was sold to Mexico. She was ordered as part of the "ABCD" ships, the others being the cruisers , , and . These were the first ships of what came to be called the "New Navy", representing the transition from wooden-hulled to steel-hulled warships. Like the other three, "Dolphin" was built with a sail rig (later removed) to increase the ship's cruising range due to the inefficient steam engines of the day. All were ordered from the same shipyard, John Roach & Sons of Chester, Pennsylvania. However, when Secretary of the Navy William C. Whitney initially refused to accept "Dolphin", claiming her design was defective, the Roach yard went bankrupt and the remaining three ships were completed in navy yards that had little experience with steel-hulled ships. Built for speed at the expense of protection, "Dolphin" was unarmored and her engine was unprotected as it extended above the waterline.