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The largest, most numerous and last of the US Navy’s second-generation ASW escorts were 46 ships of the Knox class. Planned as follow-ons either to the 5-inch gun Garcia class or to its Tarter missile-equipped Brooke class variant, their initial design incorporated their predecessors’ pressure-fired boilers in a similar-sized hull designed around the massive bow-mounted SQS-26 sonar. When the time came in 1962, in light of the Tartar’s prospective cost and anticipating that larger types would satisfy the Navy’s future guided missile needs, Defense Secretary Robert McNamara chose the gun design—with a single 5-inch/54 rapid fire weapon (introduced in the Mitschers a decade earlier) that, on paper, surpassed in firepower the Garcias’ two tried-and-true 5-inch/38s. Ten ships were authorized in fiscal year 1964, sixteen in 1965 and ten each in 1966, ’67 and ’68; six were canceled in 1968 and four more in 1969. Built by four yards and commissioned as destroyer escorts (DEs) 1052–97 in 1969–74, they were redesignated frigates (FF) on 30 June 1975.

The Knoxes were the US Navy’s last destroyer-type design with a steam powerplant. In appearance, they were conspicuous for their tall, circular cross-section “macks.” They were wet forward, prompting modification with bow bulwarks and spray strakes for some ships. Most obviously, they were big: thanks in part to a late reversion to conventional 1,200 psi boilers, they gained 24 feet in overall length and twenty per cent in weight over the Garcias—which made them comparable in size to the Charles F. Adams-class guided missile destroyers and larger than the all-gun World War II and Forrest Sherman classes in the destroyer squadrons to which they were attached.

Roomier than these destroyers, the Knoxes were generally liked by crews but naturally, as specialized ASW platforms, could not match their offensive capability. The Knoxes also lacked redundancy: their single screw made breakdown a concern and their lone 5-inch/54 could jam during continuous fire (embarrassing on the Vietnam gun line when they were new). Thus inviting and suffering from side-by-side comparison with the destroyers, they became known to a generation of destroyermen as “McNamara’s Folly.”

As they aged, however, their weapons and sensors evolved significantly. In 1971–75, 31 Knoxes received the basic point missile defense system (BDPMS). Downes was subsequently modified to carry Sea Sparrow surface-to-air missile launchers. Later, all ships were upgraded with the Phalanx Mk 16 close-in weapons system (CIWS). Also, the class’s stern-facing torpedo tubes were replaced by the SQS-35 variable depth sonar and the AN/SQR-18A TACTASS towed passive sonar array plus a LAMPS Mk I SH-2D Seasprite helicopter.

Thus enhanced, the seaworthy Knoxes enjoyed a 20–25-year service life in the US Navy until they were phased out in 1991–94, when the Soviet submarine threat collapsed and after the Oliver Hazard Perry-class frigates had arrived in numbers. Not yet done, some become the core of the Innovative Concept Reserve Training Program (ICRTC), available for reactivation on 180 days’ notice. Eventually, while 34 were transferred to Turkey (12), Taiwan (8), Mexico (4), Greece (3), Thailand and Egypt (2 each), nine were scrapped and six were sunk as targets.

Knox, herself, was the last to go—towed from Bremerton, where she had been laid up, to Guam and sunk there in the summer of 2007.