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Mk 27 Mod 4 and Mk 34:1

Homing Iorpedoes in WWII

The U.S. Navy entered World War II with few torpedoes and no acoustic homing torpedoes. When the war ended in 1945, the Navy torpedo inventory contained several torpedoes including passive acoustic homing torpedoes, Mk 24, Mk 27, and Mk 28. The capture of the German G7 e torpedo demonstrated the feasibility of electric propulsion for fleet torpedoes. The quieter electric propelled torpedoes became the platform for the acoustic homing systems. The original thermal propulsion systems using oxidizers (air, enriched air, oxygen, or hydrogen peroxide) and a fuel (alcohol or kerosene) had too much internal noise for acoustic systems to be effective in these torpedoes. The aircraft launched Mk 24 torpedo, called FIDO, was the first U.S. acoustic homing torpedo (see SUBMARINE REVIEW, January 1996). It bad an electric propulsion and steering system. The passive homing system from FIDO was modified and put into the Mk 27 torpedo which was designed to be launched from submarines.

The Mk 27 Mod 0 torpedo was affectionately known as cutie. It began service as an anti-escort torpedo in late 1944 and about 100 torpedoes were fired during WWII with an efficiency of about 33 percent. A single homing torpedo could take the place of a salvo of non-homing torpedoes, thereby increasing the effectiveness of a submarine load of torpedoes. The Mk 27 was a quiet running torpedo with an electric propulsion system. It was designed as a swim out torpedo, thereby reducing the alertment noise from the alternative compressed air torpedo ejection system. It was a smaller torpedo than most submarine launched torpedoes. It had a diameter of 19 inches, 90 inch length, a weight of 720 pounds and a warhead of 95# HBX-1. It had a speed of 12 knots and a range of about 5 kiloyards. About 1000 torpedoes were eventually built by Western Electric. Because of the small warhead, this torpedo like its sister, the Mk 24, provided for mission kill versus platform kill.

The Mk 28 torpedo entered wwn at the close of the war. This was a submarine launched passive homing torpedo with a larger warhead (585#HB.) than the Mk 27. It was also larger than the Mk 27 torpedo with a diameter of 21 inches, length of 246 inches, and a speed of about 20 knots. It had a range capability of about 4 kiloyards. Although about 1700 torpedoes were built by Westinghouse, very few saw service during WWII because of its late entry into the war. This torpedo was later replaced by the Mk 37 torpedo.

The success of these passive homing torpedoes depended on fire control accuracy. Some submariners thought that they could just point in the general direction and shoot and the torpedo would find its way to the target. These torpedoes had endurance and range but the acoustic homing range was shorter depending on the target’s noise and the environment. Proper placement of these homing torpedoes relative to the target was critical to success.

There were many homing torpedoes being developed with the Mk 24 FIDO acoustic system, but most of them did not get into significant production. Some of these torpedoes were designated as the Mk 21. Mk 29, Mk 30, Mk 31, and Mk 33. Active homing was attempted in the Mk 22 but only in the horizontal plane during terminal homing. The Navy decided to stop wort on these projects and incorporate the best features into other torpedoes. Work continued on modifications to the existing torpedoes.

Non-Homing Torpedoes in WWII

The non-homing torpedoes in the Navy’s inventory at the end of WWII were the aircraft launched Mk 13, the surface ship launched Mk 15, and the submarine launched Mk 14, Mk 16, Mk 18, and Mk 23 torpedoes. The Mk 28, patterned after the German G7e torpedo, bad an electric propulsion system with a speed of 29 knots and a range of 4 kiloyards. Although it was electric, the control system used compressed air which made it somewhat noisy for acoustic homing systems. Several non-homing torpedoes were still in development, such as the Mk 16, Mk 17, Mk 19, Mk 20, Mk 23, Mk 25, Mt 26 and the Mk 29. Of these non-homing torpedoes, only the Mt 16 and Mk 23 entered production. The Mk 16 produced at Newport, Rhode Island and Forest Park, Illinois, had a length of 246 inches, weight of 2 tons, 746#HBX warhead, a speed of 46 knots, and a range of 11 kiloyards. This torpedo bad a late entry into WWII. Most of these torpedoes were produced after WWII. The Mk 23, a high speed only version of the Mk 24, was produced (9600 units) at Newport, Rhode Island during WWII, but was not used to any extent because of its short firing range requirements. Since the fuel consumption goes up on a cubic rate with speed, this torpedo had to be fired close to the target, thereby endangering the launching submarine.

Post War Homing Torpedoes

After wwn, the Navy maintained research facilities on torpedoes. Newport, Rhode Island continued testing thermal propulsion systems for torpedoes and the newly formed Ordnance Research Laboratory (ORL) at Pennsylvania State College continued research on acoustic homing torpedoes. ORL was initially staffed by many former Harvard Underwater Sound Lab (HUSL) scientists and engineers that moved to ORL after HUSL closed in 1945. ORL (now Applied Research Laboratory (ARL)) is one of four Navy sponsored university laboratories. The other laboratories are Johns Hopkins, Applied Research Lab (formerly Defense Research Lab) University of Texas, and Applied Physics Lab, University of Washington.

During the years following WWII, many innovations in torpedo development took place. The Navy was determined to maintain its technical edge. In 1946, underwater fired rockets were designed and tested at ORL Penn State with the assistance of a German scientist, Georg Knausenburger. This was the forerunner to the Polaris missile system. The scientists and engineers at ORL demonstrated successful optical wake homing torpedoes in 1947 and successful acoustic wake homing torpedoes in 1952. Work also continued on improving the passive homing systems and developing active homing systems using echo ranging techniques.

The Mk: 21 torpedo was a passive acoustic version of the aircraft launched Mk: 13 torpedo developed by HUSL and Bell Labs. Although it had a steam propulsion system, newer acoustic isolation techniques made it possible for this torpedo to operate with a passive acoustic system. This torpedo launched from aircraft was an anti-surface ship torpedo. The Mod 0 version did not make it into production. Later, ORL developed the torpedo Mk: 21 Mod 2 which was intended for use with a guided missile system. It was given a set of wings and a rocket motor and designated as the Petrel guided missile system with a range of 10 miles. Only a few hundred of these were produced.

The Mk 32 Mod 2 torpedo became the first fleet torpedo to use an active homing system. The active homing concept conceived in 1942 at HUSL was developed at ORL by the transplanted HUSL engineers. About 3300 of these torpedoes were produced to be used against submarines from either aircraft or surface ship platforms.

General Electric incorporated a combination active-passive homing system into the Mk 35 torpedo which was to be a universal torpedo capable of being launched from any platform. However, only 400 Mk 35 torpedoes were built. The Mk 35 torpedo, in service from 1949 to 1960, was replaced by the Mk 37 torpedo which was produced in quantities greater than 3000 units.

Mk 27 Mod 4 and the Mk 34-1

Near the end of the ’40s, the conflict between North Korea and South Korea was beginning to involve the U.S. The Navy was concerned that the Russians, with a large number of captured German Type XXI U-Boats at Vladivostok, may possibly enter the war on the side of the North Koreans. The Type XXI U-Boat was faster than its predecessors from WWII and could outrun a MK 27 running at 12 knots. A dependable submarine launched acoustic homing torpedo was needed. The Mk 27 torpedo was a submarine launched version of the Mk 24 (FIDO) torpedo developed at Harvard during World War II. Similar updates were needed for the aircraft launched Mk 24 torpedo. ORL was tasked by the Navy in 1948 to develop new versions of the sub launched Mk 27 and the aircraft launched Mk 24 torpedoes with significant improvements to the vacuum tube homing system, warhead, endurance, own ship safety, and torpedo electronics.

Paul Ebaugh, ORL, was the Project Engineer who had responsibility to develop the Mk 27 Mod 4 torpedo and the Mk 34-1 torpedo. There were many component changes to modify tolerances on power supplies and related homing system functions. New concepts were added to the homing system to increase the detection and tracking capability. New type gyros were used to insure torpedo dynamic stability. Larger warheads were used with improved exploders. Anti-circling safety systems were included to protect the launch ship from its own torpedo. Paul Ebaugh, Ed Ulrich, and their associates were able to complete the crash project within one year. The Navy produced 2000 Mk: 27 Mod 4 torpedoes and 4050 Mk 34-1 torpedoes at the Forest Park, Illinois facility. The first 400 Mk 27 Mod 4 torpedoes were tested at the Key West, Florida test site.

The transducers were located on the sides near the nose to make room for the exploder contact mechanism. There were four sensing elements in each transducer. later designs moved the transducers to the nose as in the first Mk 24 torpedoes. Actual homing range is dependent on acoustic propagation conditions and target characteristics, such as aspect, speed, and noise. Table 1 shows the comparison of the features of the Mk 27 Mod 0 torpedo and the Mk 27 Mod 4 torpedo. Significant improvements were increases in homing range, speed, warhead size, and component tolerances.

Table 1. Mk 27 Mod 0 and Mk 27 Mod 4 Torpedoes

Charecteristics Mk 27 Mod 0 Mk 27 Mod 4
Length 90 inches 126 inches
Weight 720 Ibs 1175 Ibs
Diameter 19 inches, 21 inchcl 19 inches guide rails 19 inches, 21 inchcl 19 inches guide rails
Propulaion Electric Electric
Homing Passive Improved Passive
Warhead 95 # HB. 128 # HB.
Speed 12 knots 16 knots
Range S kyd (12 minutes) 6.2 tyd (12 minutes)

The Mk 34-1 torpedo was a new torpedo based on the successful Mk 24 torpedo. The improved characteristics are shown in Table 2. Technology improvements and component tolerance improvements to the Mk 27 Mod 4 were also incorporated into the Mk 34-1. Significant improvements were increases in the speed, homing range, and warhead size.

Design work was also done at ORL for the fire control systems of the Mk 27 Mod 4 torpedoes as well as the Mk 34-1 torpedoes. ORL also designed the aircraft launcher for the Mk 34-1 torpedoes.

The first wire guidance used with torpedoes was in the Mk 27 Mod 4 torpedo. This new torpedo designation was called the Mk 39 Mod 1 torpedo. It carried a trailing wire for mid-course guidance through the fire control system. The Mk 27 Mod 4 and Mk 30 Mod l torpedoes remained in the fleet from 1948 to 1960 being replaced by the Mk 37 torpedo. The Mk 34-1 torpedo remained in the fleet until 1958, being replaced by the Mk 43. The Mk 39 Mod l was removed from the fleet when wire guidance was added to the Mk 37 Mod l torpedoes in the late 1950s. The Mk 37 torpedo development will be discussed in a future SUBMARINE REVIEW.

Table 2. Mk 24 and the Mk 34-1 Torpedoes

Characteristics Mk 24 Torpedo Mk 34-1 Torpedo
Length 86 inches 125 inches
Weight 680 Ibs. llSO Ibs.
Diameter 19 inches 19 inches (21 inch guide rails)
Propulation Electric Electric
Homing Passive Circle Search Passive Circle Search
Warhead 92 # HBS 116 # HBS
Speed 12 knots Search-11 knots
Homins-17 knots
Range 4 kyd (12 minutes) 12 kyd @ 11 knoll (30 minutes)
3.6 kyd@ 17 knots (7 minutes)

The author wishes to thank all those who provided comments relative to the writing of this article. History is easy to recon-struct, tough to verify. There is still much documentation and varied opinions on the chronological development of torpedoes. Parochial interests sometimes illuminates or shadows actual events. 1his author has made a serious attempt to weigh the multitude of information as to authenticity and to present that data in a readable format.

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