6 ships (of 26 planned) ordered under the 1935 Program were improved and enlarged versions of the 1934 and 1934A classes. Most of the serious faults of the earlier ships had been resolved: engine reliability and the structural integrity was much improved and they were much better seagoing ships, shipping less water through an improvement in the design of the bows. Despite this, five of this newer type were also lost at Narvik in April 1940. Zerstörer 1936A "Narvik" Eight destroyers intended to carry new 150 mm (5.9 inch) guns in single turrets with a twin turret at the bow. The twin mountings were not ready in time and so singles were first used, and the twins fitted later. Anti-aircraft armament was substantially improved. Despite reusing earlier ship designs as a basis, with modifications to improve seaworthiness, the ships were wet in heavy seas, especially fitted with heavy turrets. After much effort, the problem was traced to a newly designed stern. However, this problem was somewhat offset by the fact that the twin mount was fully enclosed and had a high maximum elevation, allowing limited use against aircraft. These ships reverted to the traditional German practice of giving torpedo ships numbers rather than names. Four survived the war. Zerstörer 1936A (Mob) When war broke out in 1939, planned new destroyer classes were cancelled and twelve additional 1936A vessels (Z.31 to Z.42, although the last three were to be cancelled) were ordered with slight modifications to speed construction and save materials. "Mob" stands for "Mobilmachung" (Mobilisation). The 150 mm twin turrets had been manufactured for planned, but never built, "O" class battlecruisers. In war service, the engines were more reliable than in earlier ships but at the end of the war, heavy corrosion was discovered. Seven of this sub-class were built: one was sunk, another two were severely damaged and not repaired. The remaining four were war booty allocated to the Allies. Zerstörer 1936B The main armament of this class reduced back to single mounted 128 mm guns and the anti-aircraft armament was increased. The efficacy of this change was not proven in high seas as this sub-class only operated in the Baltic and coastal waters. Eight ships to this design were ordered, but the orders for Z.40, Z.41 and Z.42 (all three ordered from Germaniawerft at Kiel) were replaced by orders for three Spähkreuzer ("scout cruisers"), to be numbered Sp.1,