It referred to the battleships of the early 1900's. These
massive war machines were pretty much invincible and "feared
nothing," in otherwords, they were in 'dread of nought.' They were
armed with large-caliber guns in turrets. The name alludes to HMS
Dreadnought, a ship launched by Britain in 1906.
A dreadnought was a British name for an large ironclad,
steam-powered warship with a lot of big guns on it. Later the term
was changed to battleship.
A dreadnought is type of battleship, built after 1906, that
utilized an "all-big-gun" arrangement. Dreadnoughts usually only
had eight or more, 12 inch guns, where pre-Dreadnought battleships
usually only carried four 12 inc guns, and an assortment of smaller
guns.
One good example of this new type of battle ship was the HMS
Tiger.