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The Russian Navy’s landing ship Ivan Gren with her hull wrapped in electric cables to deperm it. Deperming helps to stop interference with communication and navigation equipment, and to counter magnetic mines.
Personnel of the United States Navy’s aircraft carrier USS Harry S. Truman pulling an electric cable across the flight deck during a deperming operation

de- (prefix indicating removal or reversal) +‎ perm(anent magnet).[1]



deperm (third-person singular simple present deperms, present participle deperming, simple past and past participle depermed)

  1. (transitive, chiefly nautical) To degauss or demagnetize; especially, to degauss a ship by dragging a large powered electrical cable along its side.
    Synonym: wipe
    • 1948, The School Science Review: A Magazine for Science Teachers, volume 30, London: John Murray for the Science Masters' Association and the Association of Women Science Teachers, →ISSN, →OCLC, page 46:
      Vessels wiped and depermed as outlined above were found to age towards their original state, so the processes as described were only effective for comparatively short periods and had to be repeated at regular intervals.
    • 1964 June, Manual for Fluxgate Ferrite Magnetometer (CRSR; 172), Ithaca, N.Y.: Center for Radiophysics and Space Research, Cornell University, →OCLC, page 6:
      Our present system deperms more reliably and is arranged to deperm the sensor each time the power source for the magnetometer is turned on.
    • 1966 April, C[hester] L. Parsons, C. A. Harris, “Appendix C: Test Procedure”, in IMP-I Spacecraft Magnetic Test Program (NASA Technical Note; D-3376)‎[1], Washington, D.C.: National Aeronautics and Space Administration, →OCLC, archived from the original on 12 March 2017, page 33:
      When it is not possible to deperm the assembly below 95% of the post exposure magnitude, ascertain if the component contains parts with permanent magnets such as relays which would not deperm in the 50 gauss field.
    • 2008, M. Ludlam et al., “The THEMIS Magnetic Cleanliness Program”, in J[ames] L. Burch, V[assilis] Angelopoulos, editors, The THEMIS Mission: [], [New York, N.Y.]: Springer Science+Business Media, published 2009, →DOI, →ISBN, section 4 (Unit Testing), page 176:
      Deperming the boards individually lead to a significant decrease in the magnetic moment of the whole unit, this was then repeated on all units.


Derived terms[edit]



deperm (plural deperms)

  1. (chiefly nautical) The act or process of deperming.
    • 1948, The School Science Review: A Magazine for Science Teachers, volume 30, London: John Murray for the Science Masters' Association and the Association of Women Science Teachers, →ISSN, →OCLC, page 46:
      Fortunately a very pronounced extension of life was found to be possible for wipes and deperms by making the initial current very strong so that, for example, a positive component was made a larger negative one before being reduced to zero []
    • 1968 December 23, A. W. Fihelly, “Appendix III: Memorandum by A. W. Fihelly re SNAP-19 S/N 009 Magnetic Moments Measurement”, in W[illia]m S. West, J. Michael Holman, Herbert W. Bilsky, Techniques for Achieving Magnetic Cleanliness on Deep-space Missions: A Report Covering Task III Effort under the Study: NASA Evaluation with Models of Optimized Nuclear Spacecraft (NEW MOONS)[2], Greenbelt, Md.: Goddard Space Flight Center, published April 1969, →OCLC, archived from the original on 3 March 2017, pages III-3–III-4:
      One interesting feature of the S/N 008A and S/N 009 data is that the residual moment after deperms one through three increased from 735 to 870 pole-cm for S/N 008A, but decreased from 854 to 659 pole-cm for S/N 009.



  1. ^ deperm, v.”, in OED Online Paid subscription required, Oxford, Oxfordshire: Oxford University Press, 1972.

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