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Difficulty: HardAuthor's Primary Purpose

Steel-hulled naval vessels inevitably acquire a permanent magnetic signature during construction through mechanical stress in Earth's geomagnetic field, while also exhibiting an induced magnetic field that fluctuates with heading and latitude. Because magnetic influence sea mines detect localized distortions in the geomagnetic field caused by these combined signatures, warships utilize degaussing coils—networks of electrical cables running throughout the hull. By precisely adjusting direct current through these coils, the ship generates counter-magnetic fields that actively cancel both permanent and induced magnetic anomalies. While degaussing cannot render a vessel completely invisible to magnetic sensors, its systematic calibration drastically reduces the trigger radius of underwater munitions, significantly improving survivability in contested waters.

Which of the following best describes the author's primary purpose in this passage?

  1. A
    to describe how mechanical stress during construction imparts permanent magnetism to steel hulls
  2. to explain how degaussing systems reduce a warship's vulnerability to magnetic influence minesAnswer
  3. C
    to argue that modern naval fleets must eliminate steel hulls in favor of composite materials
  4. D
    to provide a comprehensive overview of global maritime mine warfare strategies

Answer

To explain how degaussing systems reduce a warship's vulnerability to magnetic influence mines
The passage systematically defines the danger posed by a ship's magnetic signature, details the function of degaussing coils in generating neutralizing counter-fields, and concludes with how this mitigation enhances warship survivability. Thus, the primary purpose is to explain the operational role and protective function of degaussing systems.

Step-by-Step Solution

1
Analyze the opening context and threat identification.
The text explains that steel ships possess magnetic signatures that trigger magnetic influence mines.
Establishes the foundational operational hazard addressed in the passage.
2
Identify the primary mechanism described across the body of the paragraph.
Warships use internal degaussing coils with adjustable direct currents to produce counter-magnetic fields that cancel magnetic distortions.
Highlights the main subject and operational process that the author details.
3
Synthesize the concluding summary to determine the overarching intent.
The author concludes that degaussing calibration reduces mine trigger ranges and improves vessel survivability.
Confirms that the primary communicative purpose is to explain how degaussing operates to protect vessels from magnetic threats.

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Author's Primary Purpose
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