The external torpedo tubes were omitted and the boats had a redesigned stern to reduce cavitation and on some of the boats a new bow shape was introduced to reduce the bow wave; the hydroplanes were enlarged for better submerged handling. The First World War-vintage 12-pounder was retained but replaced on Unbeaten and Unique by a 3-inch gun.
The external torpedo tubes were eliminated, and the boats had a revised stern to minimize cavitation; on some boats, a new bow design was introduced to reduce the bow wave. The hydroplanes were enlarged for improved submerged performance. The First World War-era 12-pounder gun remained but was replaced by a 3-inch gun on Unbeaten and Unique.