In response to the increase use of submarines in the events of World War 2, active sonar was implemented into the US Navy. Since submarines emerging under water were not able to be detected by radar, improvements in sonar were produced in order to achieve technology to keep up with the increasing speeds of submarines. Two types of sonar were implemented into Navy ships during World War 2, active sonar and passive sonar. Passive sonar only receives sound waves but cannot emit them.1 By receiving the sound waves, engines of surrounding ships can be determined as well as objects in the water. Active sonar consists of transmitting sound waves and receiving them.2 It is used for measuring the length of time for a sound to be reflected back to get the time it takes for the sound pulse to reach the object, determining distance and range. The electrical energy from the transmitter converts into acoustic energy which allows the transducer, the part that turns electricity into sound, to send and receive sound signals.3 The United States navy used more than just surface ships, as submarines were also used as an effort to combat the German submarines. Through the use of passive sonar, torpedoes were specifically aimed in combat. Four high frequency hydrophones are located symmetrically on the torpedo with one pair on the horizontal plane with inclined axis at equal angles to the left and right, and a second pair on the vertical axis.4 This allows the detected signals to align where the target echoes, creating the crash point of the torpedo. On the other hand, active sonar is used to detect oncoming torpedoes. As the frequency of pings from the sonar increases, it begins to indicate that the torpedo is closing in distance. Then the weapon detonates and shoots for the strike.
An instance of the implementation of active sonar in a similar situation in regards to the events of World War 2 was seen with the Battle of the Pacific. The Battle of the Pacific was the longest battle of World War 2. It began immediately upon the British declaration of war against Germany in September 1939 and ended with Germany’s surrender to the Allies in May 1945.5 The German’s took it upon themselves to declare unrestricted submarine warfare with their U-boats. The fast and hidden underwater submarines were equipped with torpedoes to vandalize and destroy the allied surface ships. In order for the US navy to defend themselves from the oncoming torpedoes, active sonar is turned on to emit sound waves as a method of determining the speed and location the torpedo is targeting.6 By turning on active sonar, the location of the navy ship is also portrayed to the other ships that have sonar turned on. This means that the exact location of the US ship is revealed to enemy ships. This is a demonstration of the clear between active sonar and passive sonar. When a battle ship wants to become invisible in clear open water, their active sonar is turned off. This means that they do not emit any signals, thus not allowing enemy ships to pick up on those absent signals.
The tactics used in the Battle of the Atlantic illustrates an example of manipulating the uses of sonar. Usually, U-boats have increased speeds and faster turn speeds than surface ships.7 Therefore, the U-boats have the ability to depth charge attack and hide under the ships. This causes a loss in sonar connection as the sound waves attempt to find the underwater source to bounce off of, but cannot since it is hiding in plain sight. The United States participated in World War 2 with an alliance with Britain and their Royal Navy. The commander F. J. Walker of the royal navy developed an anti-submarine tactic named the creeping attack technique.8 Used in conjunction with the United States army, it allowed a plan in which one ship tracks the German U-boats while a second ship attacks. Therefore by using active sonar, the location of the enemy ship is tracked. This shows the importance of sonar and how it gives an advantage to the United States Navy such as how it helped distinguish the position of the enemy during World War 2.
Limitations of Sonar
Another method in which active sonar is used, is through the strategic placement of underwater weapons. Mines are explosives placed underwater that detonate when movement is passed above it, typically used to prevent the enemy from entering a specific zone.9 Having the capability to stay active underwater for a long time, naval ships have to be on the constant look out for these dangerous objects. These mines do not emit sounds, and therefore cannot be detected by passive sonar which only has the possibility of hearing sound. Due to this, active sonar is utilized in which provides the capability to quickly and accurately defeat, classify and neutralize mines in deep or shallow environments. 10 As stated in the question, the advances in sonar technology used during World War 2 had limitations. The U.S.S. Rich sank on June 8, 1994 after striking mines. As one of the only destroyers to be lost in the United States naval invasion force, it was lost due to three mines setting off.11 Although the power of sonar allows sound detection and range detection of mines underwater, several factors distinguish a reason to which it might not have been detected. These factors include surface noise and ship noise. A main component of sonar usage correlates with sound. The surface noise such as ocean waves add to the possibility of not determining the correct sound of the dangerous mines. The noise of the ship inside and outside also poses as a possible circumstance that prevented the clear interpretation in the sonar detection.12 An example is seen with platform noise which comes from the flow of water across the receiving sonar signals.
1 V., Ol Shevskii V. Statistical methods in sonar. Springer, 2012.
2 Shevskii, 72
3 D’Amico, Angela, and Richard Pittenger. A Brief History of Active Sonar. Defense Technical Information Center, 2009.
4 Massa, Frank. Sonar Transducers: A History . Massa Products Corp, 1979.
5 “Destroyer Escorts in the Atlantic.” Battle of the Atlantic, Destroyer Escort Historical Museum, 2010.
6 Massa, 45
7 Gretton, Peter, and B. B. Schofield. “Anti-Submarine Warfare.” The RUSI Journal 118.1 (1973): 3-11.
8 Zabecki, David T. World War II in Europe: An Encyclopedia. Garland, 1999.
9 Campbell, John. Naval Weapons of World War Two. Naval Institute Press, 1985.
10 Atlantic Fleet Active Sonar Training Environmental Impact Statement. Naval Facilities Engineering Command, Atlantic, 2006.
11 Smolinski, Mike. “Navsource Online: Destroyer Escort Archive.” Destroyer Escort Index DE- 695 USS RICH, NavSource Naval History, 2009
12 Campbell, 53