The English are busily employed in introducing screw propellers into their men-of-war ; and so far as their navy is concerned, are determined to be always ready for action. The first-class British line-of-battle ship Windsor Castle, a three-decker, originally constructed for a battery of one hundred and twenty guns, was, a short time since, cut asunder at midships, and lengthened twenty-three feet, to furnish a suitable space for the accommodation of screw propelling machinery. She has just been launched, and her name is changed to that of the "Duke of Wellington." She measures nearly 4,000 tons, and mounts 140 guns. With her steam facilities she is probably the most formidable as well as the largest man-of-war afloat. The largest ship in the French navy is the icrew propeller Napoleon.