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Patrol Frigate (PF) - Development

Given budget and manning constraints, Zumwalts parameters meant the PF should complement existing forces rather than become another jack-of-all-trades warship. Given the advanced ASW capabilities of the Spruances as well as the Knox-class FF1052s, the PF designers concentrated on anti-air and -surface capability. For this reason, preeminence was given to the Mk.13 missile launchercapable of firing Standard (SM1) and Harpoon missilesand the relatively new AN/SPS49 air search radar and Mk.92 fire control systems. The latter was an American version of the Dutch WM.27, an integrated network found in the Belgian, Dutch, and German navies.

As in any new warship, modifications took place as paper ideas met concrete reality. In order to make room for the missile launcher, the designers did not include an antisubmarine rocket (ASROC) launcher. Without the ASROC launcher, the frigate did not need the large and expensive AN/SQQ23 detection and tracking sonar (found on Spruances, for example) and the designers initially selected a medium-sized Canadian SQS505 sonar to take its place. Although less capable, the size and cost savings of the smaller sonar enabled the expansion of hangar facilities aft to support two helicopters. This was only possible because the SH2 Seasprite helicopter took up space a mere 12 feet 3 inches wide; 38 feet 4 inches long; and 13 feet 7 inches high.

Several features in the PFs represented new capabilities. The helicopters themselves were the light airborne multipurpose system (LAMPS I) under development in the early 1970s. The idea was to increase the frigates sphere of influence through over-the-horizon target detection, classification, and engagement. The helicoptersequipped with submarine detection gear and torpedoesused a computer data link to operate with the frigate as a submarine hunting team. In addition, the radar and ESM gear on the SH2 Seasprite would detect surface threats well beyond the frigates surface-search radar range, allowing advance warning of missile threats and over-the-horizon targeting for the frigates Harpoons. Consistent with the policy of saving money, the Naval Sea Systems Command (NavSea) settled on the Canadian Beartrap helicopter landing system until an American variant could be developed.

Although the SM1s were used for antiaircraft and, theoretically, antimissile defense, some sort of point defense weapon was also needed. Initially, this weapon was a twin 35-mm. gun but it suffered from a short barrel life. This fact ran against the grain of keeping the maintenance cycle under control, and NavSea eventually decided on an Italian Oto Melara 76-mm. mount. It was lighter and less plagued with trouble than the 3-inch/50 mounts used in Vietnam-era destroyer-escorts, only required a crew of three (compared with fourteen for the 3-inch/50), and had a high rate of fire (one shell a second).

In keeping with CNOs request for simplicity, NavSea also chose two LM2500 gas turbines instead of a traditional steam plant. These gas turbines were marine versions of the TF 39 jet engine used to power the C5A transport aircraft and DC10 commercial airliners. They were more economical than steam plants, especially as they required fewer personnel to operate, did not suffer the same age-related breakdowns, and required much less work to overhaul. Two turbines were placed amidships, topped by an air intake system, two exhaust stacks, and connected to a main gear transmission unit. Along with smaller and simpler engines, NavSea reduced shock protection redundancies andmuch to the consternation of sailors who would serve in yawing frigatesremoved a hull-fin stabilization system from consideration.

In order to lower construction costs, the Naval Ship Engineering Center, in company with Bath Iron Works, Todd Shipbuilding, and Gibbs & Cox, developed a relatively simple ship construction format. The idea, in contrast to the highly sophisticated total package process by which Spruances were constructed, was to allow any warship-capable shipyard the opportunity to bid on the project. Like the prototype destroyers of the 1950s, this approach would offer significant replacement advantages in the event of a future global war. As part of this process, the ship was broken into sixteen prefabricated units, each requiring a lift of only 200 tons. These sections could be assembled at various locations in most shipyards and brought together in a sequence best suited to the space, equipment, and workers of any particular yard.

In addition to platform cost restrictions, the Navy also implemented an integrated logistics support plan. Its purpose was to minimize shipboard maintenance, which, in addition to saving money, would help limit overall crew size. In order to accomplish this goal, off-the-shelf equipment was installed where possible (for ease of replacement) and legacy systems avoided. On the operational side, because the gas turbine was all electric, the need for the lengthy industrial periods required by steam plants was not required. It was hoped a restricted availability of four weeks every two years would replace the three- to four-month regular overhauls required by steam-driven ships.

On 24 October 1972, the Office of the Chief of Naval Operations (OPNAV) approved a design for a 445-foot long, 45 foot wide frigate with a full-load displacement of 3,400 tons. Powered by two gas-turbine engines, the frigate had a single drive shaft with a controllable reversible pitch propeller, and was capable of twenty-eight knots sustained speed. The tightly fitted design had a crew capacity of 185, a single 76-mm. gun mount, an SM1 and Harpoon capable missile launcher, ASW torpedo tubes, and hangers for two SH2D helicopters and supporting gear.



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