Definition of "dreadnaught"

Going to his heavy grego, or wrapall, or dreadnaught, which he had previously hung on a chair, he fumbled in the pockets, and produced at length a curious little deformed image with a hunch on its back, and exactly the colour of a three days' old Congo baby.

1851 November 14, Herman Melville, “chapter 3”, in Moby-Dick; or, The Whale, 1st American edition, New York, N.Y.: Harper & Brothers; London: Richard Bentley