US Navy Hunter-Killer Submarines


Bass (SSK-2) underway.


The K1 class

A multitude of problems were identified by Project Kayo and by other ASW exercises. Submarine communications were found to be completely unsatisfactory, preventing coordinated efforts with aircraft and surface ships. Also, in the SSK role sub- marines only could detect diesel submarines that were moving at high speeds (over eight knots). Although Project Kayo was soon reduced to only SubDevGru 2, the Korean War, which erupted in June 1950, increased interest in submarine ASW. The three submarines of the K1 class were completed in 1951–1952. Their anti-submarine performance was most impressive for the time: In exercises off Bermuda in 1952, the prototype K1 detected a snorkeling submarine at 30 n. miles (55.5 m) and was able to track the target for five hours. However, the small K-boats were cramped and uncomfortable, and their slow transit speed limited their being sent into forward areas during a crisis or when there were intelligence indications of a possible conflict. Criticism of their range and endurance was met by proposals to base the K- boats at friendly European and Asian ports within 1,000 n. miles (1,853 km) of their patrol areas, and to employ submarine tankers (SSO) to refuel them—while submerged—on station.

But their ability to detect a snorkeling submarine at long range was not enough. If Soviet submarines could transit through critical areas submerged on battery/electric power or had a closed-cycle propulsion system, they would likely evade K-boat detection. And the SSKs would be severely limited by weaknesses in SSK-to-SSK communications and the short range of their torpedoes. An epitaph to the K-boats was written by Captain Ned Kellogg, who had served aboard the K3 as a young officer:

Some of the good features of the class were its simplicity . . . . It had a dry induction mast, no main induction valve . . . no conning tower and therefore no safety tank, no low pressure blower for the ballast tanks, instead a diesel exhaust blow system similar to what the German submarine force used during World War II, a simple remotely operated electrical control panel which kept the battery always available for propulsion, the newest fire control system . . . all AC power rather than split between AC and DC.

But the submarine suffered from having diesel engines that were difficult to maintain, an unreliable and insufficient fresh water plant, undependable electrical generators, and slow speed. Kellogg’s conclusion: “You just can’t build an inexpensive submarine that is worth much at all, unless you man her with a crew of courage and heart.”

“hunter-killer” submarines (SSK)

As early as 1946 the U. S. Navy’s Operational Evaluation Group had proposed the use of submarines in ASW, and that September the chairman of the planning group for the Submarine Officers Conference noted that “with the further development and construction in effective numbers of new submarines by any foreign power the employment of our sub- marines in anti-submarine work may well become imperative.” Also in 1946 the Navy’s ASW Conference proposed equal priority for a specialized, small ASW submarine as well as the new attack submarine (i. e., Tang).

The specialized “hunter-killer” submarines (SSK) would lay in wait to ambush enemy submarines off Soviet ports and in channels and straits where Soviet submarines would transit—on the surface or snorkeling—en route to and from the Atlantic shipping routes. The concept of specialized ASW submarines date to the British “R” class of World War I, when ten hunter-killer submarines were built, all launched in 1918 with only one being completed in time to see active service. In the U. S. Navy the use of an ASW submarine was proposed in a 1946 report of the Navy’s Operational Evaluation Group. The proposal resulted from the erroneous belief that the Japanese had sunk several U. S. submarines in World War II by employing such craft.

A series of Navy ASW conferences and exercises that began in 1947 in both the U. S. Atlantic and Pacific Fleets led to proposals for a hunter-killer submarine (SSK) force to counter the Soviet under- sea fleet. The central component of the American SSK design was long-range, passive sonar, which would be coupled with effective torpedoes that “would destroy any submarine which passed with- in detection range” with a very high degree of probability. The SSK was envisioned as a relatively small, simply constructed submarine capable of mass production by shipyards not previously engaged in building submarines. Several SSK preliminary designs were developed; the smallest would have had a surface dis- placement of only 250 tons, with a large sonar, minimal torpedo armament, and a crew of two officers and 12 enlisted men. The Chief of Naval Operations (CNO) initially accepted a proposal for a sub- marine of 450 tons with a pressure hull 14 feet (4.27m) in diameter, but further study by the Submarine Officers Conference revealed that the submerged endurance of this submarine would be wholly inadequate. To provide sufficient endurance the SSK characteristics ultimately approved by the CNO, on 27 May 1948, provided for a surface displacement of 740 tons—close to the German Type VII—with a pressure hull diameter of 15 1 / 2 feet (4.65 m).

The principal SSK sonar was the large BQR-4, the first array sonar developed by the U. S. Navy. Produced by the Edo Corporation, this was an enlarged version of the GHG/BQR-2 sonar. The BQR-4 had 58 hydrophones, each ten feet (3.0 m) high, mounted in a circular arrangement, similar to the BQR-2. These both had significant advantages over earlier, simple, horizontal-line hydrophones. It was more sensitive to the direction of a target, and, the electronic steering (by directing the sonar beams) rather than being mechanically trained was a quieter process.

Early SSK design sketches showed an array of the BQR-4 hydrophones ten-feet (3-m) long wrapped around the submarine’s sail structure. The final SSK configuration placed the sonar in a dome at the extreme bow of the submarine, as far as possible from the noise-generating machinery and propellers of the submarine. The estimated passive (listening) range of the BQR-4 was up to 20 n. miles (37 km) against a surfaced or snorkeling submarine (i. e., using diesel engines). Under perfect conditions, ranges out to 35 n. miles (65 km) were expected. The BQR-4 could track targets to within five degrees of accuracy. Of course, effective U. S. torpedo ranges at the time were a few thousand yards, far short of expected target detection ranges. And, the SSK’s slow submerged speed—8.5 knots—would make it difficult to close with targets detected at greater ranges.


The massive BQR-4 in the SSKs would be supplemented by the high-frequency BQR-2—a copy of the German GHG—mounted in a keel dome, as in the Type XXI[1]. The BQR-2 had 48 hydrophones forming a circle eight feet (2.44 m) in diameter. It was credited with ranges up to ten n. miles (18.5 km) with a bearing accuracy of 1 / 10 th of a degree, making it useful for fire control in torpedo attacks. Also fitted in the SSK would be the small BQR-3, an improved version of the U. S. Navy’s wartime JT passive sonar, intended as a backup for the newer sets. The small, active BQS-3 sonar would be fitted to transmit an acoustic “ping” toward a target submarine to obtain a precise measurement of range. Also, a hydrophone suspended by cable from the submarine to provide long-range, non-directional listening was planned, but not installed. With some 1,000 feet (305 m) of cable, the hydrophone could be lowered away from submarine-generated noises. A key factor in SSK effectiveness was to be self- quieting, with very quiet refrigeration and air- conditioning equipment being specially developed.

A Navy analysis indicated that a “minimum” of 25 to 70 surface ships would be required on station per 100 n. miles (185 km) of barrier to pose more than a negligible threat to snorkeling submarines. In comparison, three to five SSKs per 100 miles could be expected to detect practically all of the transiting submarines. The Navy’s SSK proposal of 1948 to meet the perceived threat of 2,000 modern Soviet submarines in the 1960s called for 964 hunter-killer boats! This number included SSKs in transit to and from patrol areas, undergoing overhaul, and being rearmed SSK armament would consist of four bow torpedo tubes with eight torpedoes being carried. The submarine would carry straight-running Mk 16 torpedoes and the new, acoustic-homing Mk 35. The latter, which entered service in 1949, was primarily an anti-surface ship weapon. The Mk 16 had a speed of 46 knots and a range of 11,000 yards (10,060 m); the smaller Mk 35 had a speed of only 27 knots for 15,000 yards (13,700 m).

The tactics envisioned the killer submarines operating in forward areas, virtually motionless and hence noiseless when on their patrol station, seeking to detect Soviet submarines transiting to ocean areas. One method considered for hovering on station was to employ an anchor for buoyancy control. With an operating depth of 400 feet (120 m), the K-boats would be able to anchor in water as deep as 3,400 feet (1,040 m). The SSKs also were intended for operation in Arctic waters in the marginal-ice area, with fathometers being fitted in the keel and atop the sail.

The SSK concept provided for a retractable buoy for radio communications with other SSKs. Two submarines in contact would be able to solve torpedo fire control solutions using only bearings (i. e., passive sonar). Congress authorized construction of the first SSK—to be “named” K1—in fiscal year 1948 (which began on 30 June 1947) and two more were authorized the following year. These three K- boats were authorized in place of one additional Tang-class submarine. To mature the K-boat design before it was turned over to non-submarine shipyards, the K1 was ordered from the privately owned Electric Boat yard (Groton, Connecticut), while the K2 and K3 were ordered from the Mare Island Naval Shipyard (near San Francisco). Proposals to build some of this trio at the New York Shipbuild- ing yard in Camden, New Jersey, did not work out. In 1948 the Navy planned a most ambitious construction program for both the K1 and Tang classes; these submarines would be in addition to several special-purpose undersea craft and a large fleet boat conversion program. Construction rates of the Tang-class would increase in 1960 to begin replacing GUPPYs that would be retired.

[1] The Type XXI’s torpedoes consisted of the Lüt, a pattern-running torpedo, and the T11, a passive acoustic homing weapon. The latter was believed to be immune to the “Foxer” and other acoustic decoys used by the Allies. Under development for future U-boat use were active acoustic homing and wire-guided torpedoes. To help the Type XXI detect hostile ships, the submarine was fitted with radar and the so-called GHG sonar, the most advanced acoustic detection system in service with any navy. The sonar was mounted in an under-keel “balcony,” and hence was referred to as Balkon.

The GHG was key to an advanced fire control system fitted in the Type XXI. The submarine’s echo- ranging gear and plotting table, specifically designed for such attacks, were linked to a special device for so-called “programmed firing” in attacking convoys. As soon as a U-boat had succeeded in getting beneath a convoy, data collected by sonar was converted and automatically set in the Lüt torpedoes, which were then fired in spreads of six. After launching, the torpedoes fanned out until their spread covered the extent of the convoy, when they began running loops across its mean course. In this manner the torpedoes covered the entire convoy. In theory these torpedoes were certain of hitting six ships of from 197 to 328 feet (60 to 100 m) in length with the theoretical success rate of 95 to 99 percent. In firing trials such high scores were in fact achieved.


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