USS Assurance (AM-521/MSO-521) was an Ability-class minesweeper acquired by the U.S. Navy for the task of removing mines that had been placed in the water to prevent the safe passage of ships.

The first ship to be named Assurance by the Navy, MSO-521 was laid down on 28 January 1957 at Sturgeon Bay, Wisconsin, by Peterson Builders, Inc.; launched on 31 August 1957; sponsored by Mrs. Vernon W. Thomson; and commissioned at Boston, Massachusetts, on 21 November 1958.

While taking part in numerous minesweeping exercises, she visited ports along the U.S. East Coast, on the Gulf of Mexico and in the Caribbean into the following summer.

She operated in the Panama City area until 9 February 1962, when she sailed for the Mediterranean and visited ports in Sicily, Greece, Crete, Italy, Spain, and France.

After three months of service and a short tender availability, Assurance sailed on 1 October with MinDiv 81 for a tour in the Mediterranean.

She took part in Operation "Steel Pike II," then put into Málaga, Spain, before moving to Naples, Italy.

After stops in Toulon, France, and Santa Manza, Corsica, Assurance proceeded to Sanremo, Italy, for the Christmas holidays.

Upon her return to Panama City in March, she resumed work for the Mine Defense Laboratory before entering the Charleston Naval Shipyard in July for an overhaul.

Assurance sailed to Charleston, South Carolina, on 11 January 1967 for interim overhaul and returned to her home port on 11 March to commence type training.

In October, Assurance was at Pensacola, Florida, for a restricted availability before finishing the year in port at Panama City.

After her arrival in Panama City on 16 June, she spent the next four months in local operations and, on 13 November 1969, commenced an overhaul at Charleston that lasted until early April 1970.

On 26 April, the minesweeper got underway for refresher training; but, that same day, she suffered a major engine casualty and was forced to return to port for repairs which lasted three months.

The ship got underway again on 2 August, successfully completed all phases of her training by 5 October, and rejoined the U.S. Atlantic Fleet.

She provided services to the Fleet Mine Warfare Training Center at Charleston and conducted minesweeping exercises before sailing to Florida's Cape Kennedy, to support the launching of the Apollo 17 space shot.

On the 23d, she sailed to Fort George Island, Florida, for overhaul by the Atlantic Drydock Corp. During this work, her minesweeping gear was removed.

Her overhaul was finished on 11 November; and, on 3 December, Assurance got underway for Guantánamo Bay, Cuba, and refresher training.

She conducted special operations in the western Atlantic Ocean from 15 April through 14 June and, after a brief visit to Halifax, Nova Scotia, returned to Charleston.