and excellent cross-country capabilities; the CKD was 8.5 tons and also fitted with a 37 mm gun - due to extensive tests it was an extremely reliable machine with a top quality chassis. Both were taken into the German panzer forces, as the PzKpfw 35(t) and the PzKpfw 38(t), and further production was ordered. CKD was renamed Böhmisch-Mährische Maschinenfabrik AG (BMM) in 1940 and continued production until 1942, providing the Wehrmacht with 1,168 PzKpfw 38(t)'s. In 1940 Czech tanks made up around a quarter of the entire German panzer force. Lighter tanks formed almost the entirety of the German forces, but the heavier tanks were at least in prototype. In 1934 a number of heavy prototypes were constructed, based around either 75 or 105 mm main guns. Designated Neubaufahrzeug (NbFz) and very similar to contemporary Russian and British designs six were built by Rheinmetall and Krupp. Useful for propaganda purposes these tanks did not enter production, their later designations of PzKpfw V and VI were transferred to the production Panther and Tiger types. With the knowledge of the NbFz and the experiences of the lighter tanks in Spain, German designers began to create their own designs. The PzKpfw III was the first German tank capable of firing armour-piercing rounds, although the 37 mm gun was considered underpowered but was used in the interests of standardisation with the infantry. The official German designation was Panzerkampfwagen III (abbreviated PzKpfw III) translating as "armoured battle vehicle", and it was intended to fight other armoured fighting vehicles and serve alongside the infantry-supporting Panzer IV. Limited by existing bridges to a maximum weight of 24 tons, development contracts for the Zugkraftwagen were issued late in 1936. Development work continued until 1938 when the Ausf D went into limited production, a 19-ton machine it was powered by a 12-litre engine, with a top speed of and fitted with 30 mm armour all round. By the outbreak of war around fifty had been completed and some saw service in Poland. Full-scale production did not begin until October 1939 as the Ausf E, around 350 PzKpfw IIIs in D and E variants were ready by the invasion of France. Spanish Civil War On 18 July 1936 the Spanish civil war broke out. After the chaos of the initial uprising, two sides coalesced and began to consolidate their position—the Popular front (the Republicans) and the Spanish Nationalist front. In