Following shakedown, Pinto served in Service Squadron 1, Service Force, Atlantic Fleet operating on the U.S. East Coast of the United States and at Argentia, Newfoundland until 15 December 1943 when she arrived Long Island Sound to conduct salvage and towing operations for the U.S. Army and Navy Proving Grounds, Davisville, Rhode Island.

On 26 March 1944, Pinto was underway for the European theater of operations, arriving Falmouth, England on 19 April. She was redesignated ATF-90 on 15 May. She arrived off the Normandy invasion coast on 6 June, where she and two other tugs comprised Combat Salvage Unit 122.3.1 which assisted and made emergency repairs to invasion landing craft while under enemy fire. On "D-Day" plus one (7 June 1944), Susan B. Anthony (AP-72) struck a mine, and was left burning and in a sinking condition. Pinto aided in removing 2,200 Army troops plus the Navy crew, while having to cut the lines connecting Pinto and the Susan b. Anthony with axes as the latter was pulling the former down with her, for which she received the Navy Unit Commendation. It holds the Guinness world record for most people saved with no deaths. Pinto remained on station as combat salvage vessel off "Omaha Beach" until 3 July when she returned to England.

She arrived at Oran, Algeria, on 21 July, and joined the assault Force for "Operation Dragoon". On 15 August she arrived off the coast of southern France with task unit TU 85.14.7 and conducted salvage operations under enemy fire until 28 August when she returned to Oran and then the United States.

On 10 November Pinto, with a floating drydock section in tow, got underway for Panama, whence she proceeded across the Pacific to Bora Bora, Society Islands to join the 7th Fleet. Until June 1945 Pinto engaged in towing and salvage operations off New Guinea, the Admiralties, the Philippines and Morotai. On 4 June, Pinto departed Morotai as part of task group TG 76.20 for the amphibious assault on Brunei Bay, British North Borneo. She remained as salvage tug on station in Victoria Harbour until 2 July when she returned to the Philippine Islands for towing assignments.

During autumn Pinto conducted salvage and towing operations between Morotai, Balikpapan, Tarakan and Leyte Gulf. Then in December she got underway for the United States and inactivation.

On 11 July 1946 Pinto was decommissioned and entered the Atlantic Reserve Fleet, berthed at Orange, Texas. She was transferred, 1 May 1974, cash sale, under the Security Assistance Program, to Peru, and renamed BAP Guardian Rios (ARB-123).

Pinto received the Navy Unit Commendation and also three battle stars for World War II service:

• Invasion of Normandy, 6 June to 3 July 1944
• Invasion of Southern France, 15 to 28 August 1944
• Borneo operation, Brunei Bay operation, 4 June to 5 July 1945

• This article incorporates text from the public domain Dictionary of American Naval Fighting Ships. The entry can be found here.

• Photo gallery of USS Pinto (AT-90/ATF-90) at NavSource Naval History