The second USS Mackinac (AVP-13) was a United States Navy Barnegat-class small seaplane tender in commission from 1942 to 1947 that saw service during World War II.

After three months of shakedown, Mackinac, escorting a large convoy, departed the United States West Coast for Pearl Harbor, Hawaii, on 11 May 1942, arriving there on 19 May 1942.

On 22 May 1942, the famous explorer Rear Admiral (retired) Richard E. Byrd and his staff came on board for an inspection cruise of U.S. bases in the South Pacific.

Byrd, because of his worldwide recognition, had been drawn out of retirement to represent the United States to the French colonies in the South Pacific, which were nominally under the control of the pro-German Vichy government, as their cooperation was vital to the war effort there.

Byrd debarked at Auckland, New Zealand, on 23 June 1942, and Mackinac then headed to Naval Base Noumea at Nouméa, New Caledonia, on 18 July 1942.

With preparations underway for the Guadalcanal‑Tulagi landing, scheduled for 7 August 1942 through 9 August 1942, Mackinac was assigned the task of setting up a seaplane base at Malaita, the most advanced post of the Guadalcanal campaign, while her PBY Catalina flying boats searched northward and westward to watch the sealane between Truk and Guadalcanal in case of any Imperial Japanese Navy reaction from its base at Truk.

Despite constant evacuation alerts and numerous search plane losses, Mackinac next set up base at Graciosa Harbor in the Santa Cruz Islands on 20 August 1942.

After a month of transport duty between Midway Atoll and Maui, Hawaii, Mackinac left Pearl Harbor on 20 November 1943 escorting the seaplane tender Curtiss to the Ellice Islands.

When a PBY Catalina flying boat was forced down near Nui in the Gilbert Islands, Mackinac, after locating it early on 24 November 1943, rescued the crew and safely towed the plane to Fenua Tapu despite adverse weather.

Relieved at Saipan on 19 August 1944, Mackinac joined the seaplane tenders Chandeleur, Pocomoke, Yakutat, and Onslow in sailing for Kossol Passage, Peleliu, in the Palau Islands, arriving on 15 September 1944, one day after the American landings on Pelelieu.

After the seaplane group moved its operations to Okinawa on 14 July 1945, Mackinac tended motor torpedo boats through early August 1945.

Barnegat-class ships were very reliable and seaworthy and had good habitability, and the Coast Guard viewed them as ideal for ocean station duty, in which they would perform weather reporting and search and rescue tasks, once they were modified by having a balloon shelter added aft and having oceanographic equipment, an oceanographic winch, and a hydrographic winch installed.