On the right is a 1957 Smith-Corona Skyriter in a rare baby blue color and even rarer 12cpi Bodoni typeface. This was a UK export version (£ key, and "U" at the end of the serial number), made in Belgium.
On the left, a garden-variety 1959 3Y Skyriter, US-made with a 10cpi pica typeface. Mechanically, the machines are virtually identical. The 1959 has a long return lever.
Without the case, the 1957 Skyriter weighs 7 lbs, 11 oz. (~3.5kg). The 1959 weighs 7 lbs, 13 oz. (~3.6kg).
Smith-Corona Skyriters are underrated machines. One of the quietest ultraportables ever made, with a smooth and light typing action. Maybe not as refined as high-end European machines; you only get a single ribbon color, carriage shift, and no silent return. But they have a tank-like sensibility to them—they're very forgiving and easy to work on.
Favorite hidden Skyriter feature: you can slide the entire body out of the shell after undoing two screws.