USS Slater - Destory Escort Historical Museum



Destroyer Escort Weapons and Technology

Destroyer escorts mounted the latest and most up-to-date anti-submarine weapons and detection gear available during World War II, including depth charges, hedgehogs, air and surface search radar, sonar, and a high frequency radio direction finder known as HF/DF. Destroyer escorts also carried a sophisticated control station for this technology known as the combat information center. The ships mounted hedgehog ahead-thrown depth charges and conventional depth charges for attacking submerged boats, as well as large and small caliber deck guns. All of these technologies are preserved intact aboard the SLATER today.

Radar transmitted microwave beams in a straight line through the air. When these beams struck an object, reflected energy returned to and was captured by the radar antennas. The effective range of search radars was extended by placing the surface and air antennas high on top of the ship's mast. Targets could be detected by radar long before visual sightings were made. This reflected information was displayed on radar scopes as the contact's bearing and range. Radarmen plotted this information and, with a series of plots over time, could determine the contact's course and speed.

Radar was one of the most important innovations of World War II. Sets mounted onboard ships early in World War II could barely detect a large ship and had very little chance of finding the small conning tower of a submarine. However, radar technology evolved rapidly during the war and improved sets were installed on ships frequently. By the time the SLATER was commissioned in 1944, its radar sets could detect airplanes almost ninety miles away and a U-boat's periscope at two miles away. The radar sets currently mounted onboard the ship, an SA air search set and SL surface search set, are the same types carried by the SLATER during World War II.1

Sonar was a destroyer escort's only means of detecting a submerged submarine. A sound wave was transmitted through the water. An object in the water caused an echo to return. The operator used the time the echo took to return to estimate the distance to a potential target. Sonar technology improved dramatically during the course of World War II, but it was still markedly inferior to sonar equipment in use today. The sonar set carried onboard the USS SLATER, designated QGB, was similar to a searchlight beam in that it scanned only a small area at one time, and that it had to be constantly shifted manually to scan the whole area ahead of a ship.2

Upon the SLATER's return from Greece, the sonar room had been gutted and a postwar SQS-4 sonar stack was in place in the lower sound room. This sonar set has been restored to working condition by SLATER volunteers. In addition, a World War II QGB set from the USS LOESER DE680, identical to that carried by the SLATER, was donated to the museum in 2006. This set was installed in its original location in the SLATER's upper sound room on the flying bridge. Other sonar equipment, including a bulkhead mounted attack plotter and tactical range recorder, are installed in their original positions in the sound room.

One of the most important technological developments of World War II resulted in the HF/DF detection gear. HF/DF stood for high frequency direction finder, but was most commonly known as Huff Duff. This detection gear was installed on Allied escort ships and found at land based listening stations during WWII. Huff Duff was developed to intercept Nazi U-boat transmissions. Nazi strategy called for U-boats to keep in constant radio contact with U-boat headquarters in France. They radioed convoy contact and weather reports and received their operating instructions.

By intercepting these transmissions, the Allies were able to determine the direction, or line of position of the U-boat relative to the receiving ship or land installation. If two or more allied ships or land facilities in different locations intercepted the same transmission, it was possible to triangulate the U-boat's position. Convoys could thus be rerouted to avoid the submarines. Allied hunter killer groups, many of them including destroyer escorts, could then locate and attack the U-boat wolf packs. (A wolf pack refers to a group of German subs traveling and operating together, thus increasing their ability to cause damage to a convoy). HF/DF intercepts were responsible for nearly one quarter of all U-boat losses during World War II.

The actual Huff Duff equipment consisted of a tall radio antenna carried aft of the stack. The radio receiver and scope were located at the operator's station in a compartment in the aft deckhouse on destroyer escorts. Although the SLATER itself never carried a HF/DF set, the equipment currently on display in the ship is the last Huff Duff set known to exist. Given the significance of HF/DF to the Allied victory in World War II, the set is displayed onboard the SLATER in the location that it would have been mounted on other destroyer escorts. 3

The efforts of the radar, sonar and HF/DF operators on destroyer escorts were coordinated by a station known as the Combat Information Center or CIC. This was an area abaft the bridge and under the flying bridge that housed the radar equipment, plotting tables, internal and external communications gear, and various other status and plotting boards. CIC received, evaluated and plotted on a universal drafting machine all information from sonar, radar, bridge, lookouts, radio, semaphore flags or signal lights, and anything else pertinent. It then fed data and recommendations to the captain on the flying bridge to assist him in his decisions.

In addition to tracking air and sea contacts and reporting their course and speed, CIC also assisted in station keeping, fire control, shore bombardment, navigation and search and rescue. The CIC was the nerve center and eyes of the ship whenever the ship was underway by night, day, fog, rain, snow or clear skies. The value of the Combat Information Center in the destruction of enemy submarines was considerable.

Once a destroyer escort detected a submarine, it could attack with hedgehogs and depth charges. The hedgehog projector was designed to fire twenty-four projectiles at a submarine ahead of a destroyer escort while the ship still had sonar contact with the target. World War II sonar scanned only ahead, so contact was always lost when an attacking ship got over the submarine in order to drop depth charges. The hedgehog projector solved this problem. Hedgehog projectiles were loaded on a launcher consisting of cylindrical bars called spigots, attached to cradles, which swung about a fore and aft axis by means of a roll correction gear assembly mounted on a gun train indicator pedestal. The movement was limited, but it allowed the spigots to train enough to compensate for roll of the ship and to aid in leading the target. The spigots are so positioned that, when fired, the charges described an elliptical pattern of about 140 by 120 feet. Hedgehog projectiles carried a contact fuze, meaning a direct hit on the submarine was required. Nevertheless, even the small charge carried in the projectile head was lethal.4

Destroyers also carried large number of depth charges to counter submarines. There were two depth charge racks on the stern and four depth charge projectors on each side of the ship to fire depth charges outward. The depth charge, with its 300 to 600 pounds of TNT, was the traditional antisubmarine weapon. However, a depth charge barrage required a high degree of accuracy, particularly against double-hulled German U-boats. The "water hammer" effect of a 300 pound depth charge required an explosion within thirty yards of the submarine hull for damage and ten yards for a kill. The 600 pound depth charge's lethal area was considerably enlarged. During the war, the Navy introduced a new type of charge with a "teardrop" shape and tail fins, like aerial bombs, to make them sink faster. Depth charges were detonated by hydrostatic pressure, with depth set before firing. Later models also had magnetic impulse detonators which would fire when in proximity to a submarine. Japanese submarines, lacking the hull strength and depth tolerance of their German counterparts, were more vulnerable to destruction by this weapon. 5

Finally, destroyer escorts carried many guns. As noted above, destroyer escorts carried either 3"/50 main guns or 5"/38 guns. The USS SLATER, being a CANNON class, mounted three 3"/50 guns. The 3"/50 caliber dual purpose guns were mounted inside circular gun shields. The later destroyer escort classes had two 5"/38 caliber dual purpose destroyer type guns in enclosed movable gun mounts. Both types could be fired individually or by director fire control. The 3" guns were frequently criticized as lacking in penetration power against double-hulled U-boats. The 5" type was far more effective.

In addition to the above weapons, a destroyer escort had a secondary battery of about eight 20mm machine guns and one quadruple 1.1" or one twin 40mm machine gun. Although designed primarily for anti-aircraft defense, these guns were quite often effective antipersonnel weapons. They could quickly sweep an enemy gun crew off the deck of a submarine or keep men pinned down inside the conning tower of a damaged submarine on the surface. The advent of kamikazes in the Pacific induced a hurried and massive addition of 40mm, 20mm, 50 caliber and even 30 caliber machine guns. The SLATER represents this late war modification. It mounts three twin 40mm gun mounts and nine twin 20mm machine gun mounts.6

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1 Davis, Destroyer Escorts of World War II, 5; Elliot, Allied Escort Ships, 523-4.
2 For an in-depth evaluation of World War II sonar technology, see Hackmann, Willem, Seek and Strike: Sonar, Anti-Submarine Warfare and the Royal Navy, 1914-1954, London: Her Majesty's Stationery Office, 1984.
3  Andrews, Tempest, 2, 20; Elliot, Allied Escort Ships, 525-6.
4 Elliot, Allied Escort Ships, 530-1; Campbell, John, Naval Weapons of World War II, Annapolis: United States Naval Institute Press, 1985, 91-2.
5  Ibid., 88-90; Friedman, Norman, US Naval Weapons, London: Conway Maritime Press, 1983, 122-24.
6 Roscoe, Destroyer Operations, 15-18; Friedman, Naval Weapons, 64-7, 72-3, 76-81.