You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

Category: THE CIVIL WAR 
Clue: A century before the U.S.S. Nautilus, the Confederacy had 2 of these new ships, the Pioneer  & the Hunley
submarines

Category: FUNNY HATS 
Clue: The name of this often brimless hat, popular in the 1920s, is French for "bell", after the shape of the hat
a cloche

Category: AIR APPARENT 
Clue: Thousands died in 1952 in a notorious smoggy event in this European capital

london