 Note that 7 of these vessels received 'U' names (conversely, 4 of the U class had received names beginning with 'V').The V-class submarines were very similar to the preceding U-class (short-hull) boats, of which they constituted a linear development, but had 3/4-inch pressure hull plating instead of 1/2-inch for deeper diving, also a lengthened stern and fining at the bows to reduce noise and improve underwater handling.They were sometimes referred to as "Vampire"-class submarines after .