Battle of Brunete, Battle of Bilbao, Battle of the Ebro and the Catalonia Offensive. The Nationalists developed their own light tank prototype (Verdeja) during the war, with the wide use of elements from Panzer I, and especially the T-26. Later, T-26s formed the base of the Spanish Brunete Armoured Division, serving until 1953. The T-26 was the most widely used tank of the Spanish Civil War in both armies. It was referred to as "the tank of the Spanish Civil War" in the title of one of Lucas Molina Franco's articles. "Out-gunned, out-manoeuvred, and hard-pressed, the Spanish had no effective answer to the tank", sparking several interesting developments within the context of tank design and anti-tank tactics. This was especially true regarding the T-26, given that there was no other tank in the field able to knock it out. Despite the T-26's superiority over the German Panzer I light tanks and Italian CV-33 tankettes (armed only with machine guns), the Spanish Civil War uncovered a vulnerability of the T-26 – weak armour. Even the frontal armour of the T-26 was easily penetrated by German and Italian anti-tank guns., at close ranges. Italian reports said about this vulnerability: 20 mm Italian and German guns, not effective over 400 m; 3.7 cm Pak 36, not more than 500 m; Cannone da 47/32 M35, not more than 600 m. The Italians were concerned about the powerful armament of the T-26, often used at very great ranges, up to 1,500 m. Italians rated the small and older Cannone da 65/17 modello 13 as better than the high-velocity guns they had, even if it was not used as an anti-tank gun. Greater danger was posed by the 8.8 cm FlaK 18/36/37/41 anti-aircraft gun, first deployed in those years, and capable of destroying any tank at very great range. The 15 mm bullet-proof armour of the T-26 provided little protection against it, even when firing only HE rounds. Not all Soviet military commanders recognized the T-26 light infantry tank's obsolescence in the mid-1930s and work designing tanks with antiprojectile armour was slow in the USSR at that time. Soviet-Japanese border wars 1938–1939 The first military operation of the RKKA in which T-26 light tanks participated was the Soviet-Japanese border conflict, the Battle of Lake Khasan in July 1938. The Soviet tank force consisted of the 2nd Mechanized Brigade and two separate tank battalions (the 32nd and