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Dr. Victor S. Alplier is an independent research consultant based in Austin, Texas. He is an elected member of the Society of Sigma Xi (Scientific Research Society). He has a and distinguished career as a researcher and practitioner in psychological assessment, psychopathology. He has published widely in peer-reviewed journals, including a number of recent works in militmy histolJ’ and the history of science.


Degassing is a tenn derived from the tenn gauss–measuring the strength of a magnetic field. 2 Early during WWII ( 1939), Gennany dropped hundreds of magnetic and contact mines every month into major British harbors and estuaries. Magnetic mines were also dropped that anchored themselves to the ocean floor; U- boats dropped mines from their torpedo tubes. The Empire of Japan also placed hundreds of mines monthly throughout the Pacific. Countenneasures to these hazards became an immediate high priority for the Allies. Part I of this two-part series describes the fundamentals of degaussing, and documents how Degaussing Policy (DP) was developed and implemented. Part II examines consideration of modification of DP at the height of its effective- ness in 1943. Resolution of this question led to an important final decision by the ChiefofNaval Operations in December, 1943, and thus contributed to ultimate victory in all war theatres .

Statement of the Problem: Why is Degaussing Important?

As Gennany dropped hundreds of mines in the waters around Great Britain, one mine dropped in the Thames estuary and was recovered at Shoeburyness, enabling the British to begin research aimed at developing countenneasures. Nonetheless, during the early period of the war, before the United States entered the conflict, a great deal of gross tonnage was lost at sea to magnetic mines. German mines initially detonated with a sensitivity of 15 milligauss change in the surrounding magnetic field. 3 However, some mines were equipped with counters, and would detonate after the 11′” detection, such as the 111″ pass of a vessel nearby. By early 1942, 4 milligauss magnetic and magnetic-acoustic mines had been discovered- and this was an effective increase in sensitivity by about a factor of two. Mines anchored to the seabed were of particular danger to submarines. By this time, degaussing, deperming (of submarines), and minesweeping had been im- plemented as the main countermeasures.

Ships, Submarines, Magnetism and Degaussing Policy.

All ships made primarily of metal are subject to acquired magnetization once the keel is laid. The source of initial acquired magnetism is the Earth’s own magnetic field. All vessels with metal components, even wooden minesweepers, provide low reluctance, or opposition to acquiring magnetic fields. Components of the Earth’s magnetic field are illustrated in Figure I. This one explanatory figure was used in naval manuals for decades.

A ship is basically a bar magnet with a North and South Pole. A vessel begins to acquire a magnetic signature as soon as the keel is laid. Whether or not perfectly aligned with the Earth’s magnetic field at any given location (reversed south of the equator), the ship acquires a unique magnetic signature. Then, the vessel is detectable by magnetic-induction torpedo or by the magnetic portion of magnetic-induction mines. The presence of properly degassed ships also helped to provide safe haven for submarines. Before the war, installation of coils in submarines was considered. An alternative method, flashing, became standard because of the delay required for installation of degaussing coils, and is described below. The complex series of countermeasures became functional as a component of overarching Degaussing Policy (DP), controlled by the Chief of Naval Operations (CNO) .

Including components of the Earth’s magnetic field, other factors will contribute to induced magnetic fields of surface vessels, and where applicable, submarines, which require countermeasures to their magnetic signatures. These include the firing of a ship’s guns (for example, the 16 inch guns on a battleship), firing torpedoes, the pounding of the ocean waves upon the vessel, changing barometric pressure, variations in the salinity of the water, firing of antiaircraft guns, depth charges near submarines, and the flow of current in various electric circuits and machinery aboard. Ambient air and water temperature also affected the magnetic signature.

Development of Degaussing Policy

Degaussing Policy in place when the US declared war on the Empire of Japan was a work in progress. In October, 1940, a conference was held at the Puget Sound Navy Yard concerning the installation of degaussing coils on many naval vessels, over a year before Pearl Harbor. This report not only describes problems with designing retrofitting at the Navy Yard, but also problems disseminating information to private shipyards and contractors in the Seattle area. 4 Admiral W. H. P. Blandy noted strongly in a BuOrd CONFIDENTIAL memorandum received 23 December 1941 to the Chief of Naval Operations, that

“the Bureaus (BuShips and BuOrd) recommend that degaussing coil installations be regarded as a matter of vital military necessity and that such installations be made as rapidly as circumstances permit. It is further recommended that if necessary on new construction vessels, reasonable delays in completion be permitted where such delay will result in satisfactory completion of the coiling installation prior to delivery of the ves- sel. ”

At this early point in the war, vessels without degaussing coils were being retrofitted, and new vessels were being fitted with coils integral to the design. Installation of coils on submarines caused delays in production, and was eventually abandoned in favor of a different method, described below.

Atlantic Fleet Confidential Memorandum 7 CM-42 Dated 20 January 1942 refers to a BuOrd Conference Letter dated 7 January 1942, which tends to support minesweepers in view of the initial threat of the new 4 milligauss mines, concluding that “The situation of other ships [other than minesweepers themselves] is not particularly happy [emphasis added] and there is nothing to warrant the hope they will be protected in depths much less than twice the beam in the near future …. We must, perforce, rely largely on sweeping for protection against magnetic mines.” 6 As we shall see, the view of CINCLANT, fortunately, did not prevail throughout the Fleet. As we shall see, the diverging attitudes towards the value of minesweeping versus degaussing would persist.

Fundamentals of Degaussing

Rendering a vessel magnetically invisible requires production of electromagnetic currents and is more complex than simply running one cable around the ship at the water line- although for many ships this was the lone countermeasure (and significantly, the only one employed by Germany and Japan). This is normally referred to as the M-coil; this coil is the foundation of all degaussing systems; when a coil is placed temporarily at the waterline as the flashing (demagnetizing) of a submarine, it is referred to as a Z-loop. Depending on the size of the vessel, additional coils might be installed.

Degaussing during WWII required three-watch (24 hour) monitoring of all currents and gauges by at least one Lieutenant and several electrician’s mates once installed (usually in the Engine Room). Many vessels whose keels were laid before 1941 in the United States that needed retrofitting can be seen in photographs of the decks of many WWII warships, with large bundles of degaussing cables laid around the perimeter of the deck to effect an approximation of a properly installed M-coil.

Prior to any installation, extensive testing would occur, super- vised by the Naval Ordnance Laboratory. Then, as stated by Rear Admiral H.N. Wallin, there are three activities that are critical to the degaussing of naval and merchant vessels:

1. Operation of maintenance of deperming [demagnetizing] ranges at strategic locations.
2. Design, installation, testing, and periodic inspection and repair of degaussing systems.
3. Operation and maintenance of degaussing systems on operating vessels.

Degaussing of Submarines by Flashing

Degaussing of submarines was one of the tasks of the Bureau of Ordnance. Rather than using installed degaussing coils, the solution developed was an external process, variously referred to as Flash-D, Deperming, or Flashing. Figure 2 shows a drawing of a generic submarine set up for flashing. Flash-D provides elimination of essentially all substantial permanent, induced, and acquired magnetization of the submarine, and was to be done every 6 months of operation.

Flash-D is usually done when the submarine is at a North- South magnetic heading. Following a Flash-D treatment, attention is given to potential effects on the magnetic compass. In this process, the submarine is swung for adjustment (degaussing) of the magnetic compasses before sailing, in no case prior to five hours following Flash-D. illustrate some of the further aspects of flashing submarines. Figure 5 shows USS PORPOISE with an installed degaussing coil ontside the pressure hull. As previously mentioned such coils on submarines were not standard, because of the extensive need for submarines in operation immediately at the beginning of U.S. involvement in the war. Some submarines, nonetheless, had degaussing coils fitted if this did not delay construction. The advantage was that these were continually adjusted.

In Flash-D, ever-increasing surges of power are hot-shot through the circuit, beginning at about 550 amperes, and sometimes reaching 2,000 or 3,000 amperes. For comparison, the typical output in DC transfonner to power a portable laptop computer or DVD player is 1 – 2 amperes or Jess. During the two minutes between Flash-D shots at high amperage, magnetometer measurements are taken around the ship while the coils cool. Degaussing Surface Vessels While the M-coil is the mainstay of a degaussing installation, some coils are split (e.g., F and Q coils) to provide reverse polarity in critical locations (designated as FI-QI and FP-QP coils, respectively). These splits (in series) are difficult to install but provide better neutralization of acquired pennanent magnetization . Further complicating the entire enterprise, any ship’s compass required a completely different set of compensating degaussing coils (until 1957, when it was directed that compasses be removed prior to flashing 13). Submarine tenders also were fully degaussed, as they were critical to the operation of submarines in any forward areas.

The basic layout of degaussing coils for any naval, army, or 14 merchant vessel consisted of the following: 1. M-coil (main coil): The M-coil compensated for the ship’s vertical magnetization and countering the Earth’s vertical magnetization, which is its strongest field. The M-coil (or girdle) consists of one or more horizontal loops running from bow to stem, either around the entire ship, or around the perimeter of the upper deck. This is comparable to the Z- loop used for flashing. 2. F and Q coils: Many installations also included F and Q coils (forecastle and quarterdeck coils); the F-coil covers the forward one-third to one-fourth of the ship just below the forecastle or other uppermost forward deck. The Q-coil consists of one or more horizontal loops in the after one-third to one-fourth of the ship, just beneath the quarterdeck or up- per most after deck. These F and Q coils neutralize the longitudinal (as opposed to the vertical) component of acquired magnetization. The most effective F and Q coil installations would be at different levels than the M coil.

In some cases the individual coils, not including insulation, had a diameter of over 1 inch, and might be part of a large multi- coil cable. Applied current could at some times melt the copper cable, and if there was a break or pinhole in the insulation and sailor or merchantman in the vicinity ran a risk of severe bums (Ralph A. Alpher, personal communication, 15 February 2005). Typical location of control equipment- rheostats, resistors, ammeters, reversing and disconnect switches were usually grouped together in the Engine Room. Indicator lamps and switches were placed at various locations on the ship for the benefit of crew assigned to monitor that the equipment was operating, polarity and other basic functions. I have heard of the entire operation as looking like a “Rube Goldberg” apparatus. This is significant, because, as these wires ran throughout the vessel, all personnel were aware of their protection by degaussing.

By 1943 the overall advantage was definitely with the U.S. Navy, and the submarines were well protected from mines and torpedoes detonated by magnetic influence. Deperming ranges were also built around the world for the purpose of demagnetizing submarines. By 1943, mobile ranges (barges) were also in operation. 15 Copper, Sailors, Accounting and Cost of War Liberty ships alone were using . I% of the nation’s copper, using only M coils.16 Pennies minted with a 1943 date were made of steel. Copper was an increasingly valuable commodity; the use of copper depleted existing reserves and put pressure on copper mining. Evaluation of the magnetic condition of each seagoing vessel was required at a minimum of 6-month intervals, with results to be sent immediately to the Bureau of Ordnance. This paper has given the reader a fundamental introduction and insight to the unheralded topic of degaussing. In the following paper in this series of two, we will examine the Navy’s serious consideration of reducing the breadth of what was clearly one of the most successful documented countermeasures in the purview of the Chief of Naval Operations. This would potentially affect the intricate network of defense provided to submarines and all seagoing vessels of the Navy, Army, and Merchant Marine.


Acknowledgements will follow in Part 2 of the series, to be published in the January 2011 issue of THE SUBMARINE REVIEW.


Note: In the case that a document was declassified in the conduct of my research, this is indicated in the footnote. Absent such designation, I have obtained original documents or copies of known provenance.
1. Contact Dr. Victor S. Alpher through
2. Richardson, F.D. Biographical Memoirs of the Fellows of the Royal Society: Charles Frederick Goodeve. Volume 27, 1981 ( bio.html; retrieved 17 February 2010).
3. Williamson, Gordon. (2007). U-Boats vs Destroyer Escorts. The Battle of the Atlantic. Great Britain: Osprey. Sec “Technical Specifications” chapter.
4. MEMORANDUM of Conference held at Navy Yard, Puget Sound, 1100, 10 October 1940. Subject: Degaussing Installation on various Naval Vessels. Declassified Authority NARA NND 755028, 12 October 2004. A significant purpose of surface attacks and air attacks on submarines was psychological (see Chapter 11, Report No. 51 of the Operations Evaluation Group (OEG), “Antisubmarine Warfare in World War 11″ by Charles E. Stemhill & Alan M. Thorndike, Office of the Chief of Naval Operations, Navy Department, Washington, D.C., 1946. Downgraded to UNCLASSIFIED Authority OEG, January 1962, Log. No. S-91573. Gennan U-Boats were particularly sensitive to sinking at detonations of 60 feet, regardless of actual depth setting, probably an additional effect of hydro static pressure at that depth.
5. CONFIDENTIAL memorandum, declassified NARA Authority NND 803073 14 October 2004.
An early directive from the CNO to the Chiefs of the Bureau of Ships and Bureau of Ordnance directed that submarines receive degaussing coils, only if no delay in construction would occur, in which case new and existing submarines would be degaussed by flashing. The actual number of submarines receiving degassing coils is beyond the scope of the present study, but correspondence from BuOrd and BuShips reviewed would indicated this number to be relatively small in relation to the total number of submarines serving during the conflict. CONFIDENTIAL Memorandum, Subject: Degassing-Protection of Submarines from Magnetic Mines, 10 January 1942, signed by F.J. Home, Acting CNO, declassified NARA NND 803073 14 October 2004.
6. United States Atlantic Fleet, CINCLANTFILE A2-l l/S81-6/FFl3(1) (Oil I), Naval Operating Base, U.S.S. Constellation (Flagship), 20 January 1942, over signature ofO.M. Hustvedt, Chief offstage. Distribution Atlantic List and Pacific List. Declassified Authority NARA NND 803073 14 October 2004.
7. The Bureau of Ordnance CONFIDENTIAL memorandum directing the experimental run on the U.S.S. Massachusetts to measure sources of acquired magnetism, and requesting that a Naval Ordnance Laboratory representative be permitted aboard ship to conduct the experimental measurements on board, is dated 27 March 1942 (From: The Chief of the Bureau of Ordnance; To: The Chief of Naval Operations; Subject: U.S.S. MASSACHUSETTS, BB59; Magnetic Measurements Desired – During Gunfire Tests (Declassified Authority NND 803073 NARA 14 October 2004). Ralph A. Alphcr reported to me being one of the scientifie personnel on such scientifie voyages.
8. Bureau of Ships, NA VSHIPS 250-660-34. Degaussing Manual. My personal copy is updated I 0 October 1951. However, this is essentially the same information as used during the war. It included figures dated 1942, such as the figure for ” Dimensions for Degaussing Control Rheostats & Resistors.” Sec also Bureau of Ordnance publication OP 1536, Degaussing Station Instructions: Degaussing of Submarines (First Revision, 5 November 1945; Declassified by NARA 6/30/09, Authority NND 24869). Early instructions for degaussing and deperming (Flash-D) were published with the designation DGSI (Degaussing Station Instructions). My father Ralph A. Alpher authored and co- authored many of these publications and left in his personal papers a list with the original (DGSI) designations.
9. Degaussing Station Instructions. Navy Department, Bureau of Ordnance, DGSI No. 22, which was later renumbered OP-1522, 5 October 1943. Sec p. 24. Reference is made to the original, Declassified 6/30/09, NARA Authority NND34869. Although intended for line use, this CONFIDENTIAL document states on the cover: “THESE INSTRUCTIONS MAY BE ISSUED TO PHYSICISTS CONCERNED WITH DEGAUSSING UNDER THE SAME RESTRICTIONS THAT PERTAIN TO COMMISSIONED OFFICERS. SUBJECT TO THESE RESTRICTIONS, THE RAPID DISSEMINATION OF THE INFORMATION THEREIN IS STRONGLY URGED.” The document is signed by D.W. VerPlanck (an engineer at Naval Ordnance Lab) for Admiral W.H.P. Blandy.
10. Degaussing Compass Compensating Coils Installation and Adjustment. Part I. Electrical Section, Bureau of Ships, I March 1942.
11. Handbook of Magnetic Compass Adjustment and Compensation. First Edition. Nye S. Spencer & George F. Kucera, (Lt.j.g., U.S.N.R.). Approved by the United States Navy Department Bureau of Ships, Hydrographic Office, H. 0 . No. 226. Washington, D.C.: Government Printing Office, 1944.
12. Degaussing Compass Compensating Coils (Type ” B Modified”). Electrical Section, Bureau of Ships. I November 1942. Magnetic mines continued to threaten all seagoing vessels long after the war (“30,000 Japanese Units Loose,” New York Times, 8/25/46; ” Clearing job to end next year, British Report,” New York Times, 3/3/46).
13. During WWII, rather than removing compasses from vessels during dcpcnning, they were demagnetized after depcnning. II was apparently not until 1957 that the Bureau of Ordnance ordered compasses removed during deperming. OP 1536, op.cil. (First Revision, Change I, insert change; on cover ‘Change I inscncd’ approved by the Chief of the Bureau of Ordnance, 2 Angns1 195 7.
14. Degaussing Manual. NA VSHIPS 250-660ยท34. Bureau of Ships, Navy Department. I 0 October 195 I. Earlier manuals were produced by BuShips in 1943 and revised in 1944. The essentials arc the same.
15. Mobile Depenning Station, San Francisco, California. Installation Report. April, 1943. RESTRICTED. Declassified Authority NARA NND 755028 12 October 2004.
16. This estimate appeared in a rough draft of a memorandum dated 14 April 1943, Record Group 38, NHC 39, Box 3, Declassified Authority NARA NND 907050, 14 October 2004. Memorandum concerning consideration of curtailing degassing in favor of mine sweeping during the 1943 period are marked SECRET and MOST SECRET.
17. The U.S. Navy supplied seagoing craft for such operations as Operation Overlord (the invasion of Normandy on June 6, 1944). However, the U.S. Anny maintained its own fleet of seagoing vessels. See U.S. Army Ships and Watercraft of World Warflby David H. Grover, U.S. Naval Institute Press, 1987.
18. Confidential Memorandum from the Office of the Quartermaster General (U.S. Anny) to the Chief of Naval Operations, 4 November 1940. Subject: Degaussing Equipment on Anny Vessels. The Quartermaster General was referred to the Bureau of Ordnance, for coordination with the Marine Design and Construction Section of the Office of the Quartermaster General. Declassified NARA Authority NND 755028, 12 October 2004.
19. Separate CONFIDENTIAL directives from the Commanders in Chief, Atlantic Fleet (13 April 1943), and Pacific Fleet (30 June 1943) put these requirements into effect. .
20. Refer to footnote 5 for further explanation.

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