This is a rare copy of 21st Century Sub by Frank Herbert. The front cover states "Original Title 'The Dragon in the Sea.'" Avon number G-1092. Cover price is 50 cents. Copyright 1956. Published by Doubleday under the original title, I believe this is the first paperback printing. First printing thus. This is a near fine to fine copy without wear. it is clean, straight, square, with square corners, no color loss, very slight rubbing along front edge of spine; no creases except possible single faint corner crease at front lower corner. Green edgestain. No marks or writing found. Very clean, no fingerprints or smudges. Color illustration is bright and clear, signed Art Snooman. Front cover blurb states "One of the Really Great Novels of Science Fiction"-Inside Science Fiction.

This book was written before Dune made it's author famous.