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 removed, and the sterns of the boats were redesigned to reduce cavitation; some boats also had new bow shapes introduced to diminish the bow wave. The hydroplanes were enlarged for better submerged handling. The First World War-era 12-pounder gun was retained but replaced by a 3-inch gun on Unbeaten and Unique.