Germany, Italy and the Soviet Union all experimented heavily with tank warfare during their clandestine and "volunteer" involvement in the Spanish Civil War, which saw some of the earliest examples of successful mechanized combined arms —such as when Republican troops, equipped with Soviet-supplied tanks and supported by aircraft, eventually routed Italian troops fighting for the Nationalists in the seven-day Battle of Guadalajara in 1937. However, of the nearly 700 tanks deployed during this conflict, only about 64 tanks representing the "Franco" faction and 331 from the "Republican" side were equipped with cannon, and of those 64 nearly all were World War I vintage Renault FT tanks, while the 331 Soviet supplied machines had 45mm main guns and were of 1930s manufacture. The balance of "Nationalist" tanks were machine gun armed. The primary lesson learned from this war was that machine gun armed tanks had to be equipped with cannon, with the associated armor inherent to modern tanks.