The following Italian units of the CTV participated in the fighting at Guadalajara:
The battle of Guadalaraja was essentially an Italian offensive aimed at encircling Madrid. The Italian Corpo di Truppe Volontarie (CTV) that was in Spain to aid the Nationalist cause, had recently assisted in the conquest of Málaga. Looking for martial glory, Mussolini wanted a successful Italian offensive to impress the world, despite the fact that Italy was a member of the Non-Intervention committee and, therefore, shouldn't have had troops in Spain. The Italians suggested an offensive north-east of Madrid towards Guadalajara, which they assumed would be supported by Nationalists attacks in other areas around Madrid. Franco agreed to the offensive in order to take pressure of his troops at Jarama, but did not intend to support the CTV with other attacks.
The offensive, which began on March 8th 1937, comprised 5 Italian divisions and 1 Spanish division (the Soría Division, led by the defender of the Alcázar, Colonel Moscardó.) The overall force included artillery, tanks and around 50,000 men, with the Italian infantry being motorized. At the time of the attack the Republic had approximately 10,000 men in the area, but by March 10th reinforcements arrived, bolstering their forces to around 35,000 men. These reinforcements included the men of the Garibaldi Battalion of the 12th International Brigade. The Garibaldi Battalion consisted mostly of antifascist Italians and so the Spanish Civil War would witness a mini Italian civil war.
Before the Republican reinforcements arrives, the Italians made good headway, capturing Brihuega and Trijueque. The weather at the time was very cold and rainy, creating miserable fighting conditions and also grounding the Italians air support. The Republicans were able to receive some air support as they had all-weather airfields nearby. The Republicans counterattacked on March 12th through the 15th and again on the 18th to the 22nd. The CTV's left flank gave way and the Italians began retreating in disorder. The Republicans were able to recapture most of the lost territory, including Brihuega and Trijueque. by March 23rd the fighting was over and the Italian troops were replaced by Nationalists in defensive positions. The Italians had left much equipment behind in their retreat, much of which was recovered by the Republicans. Losses on both sides were similar (around 6,000 dead and wounded), but the Republic gained a major propaganda victory that far outweighed the actual victory on the battlefield. The defeat of Italian troops, and particularly the involvement of anti-fascist Italians in that defeat, bolstered Republican morale and was viewed by many as a defeat for international fascism. Mussolini was embarrassed by the events of Guadalajara and demanded that the CTV not leave Spain until they had achieved a victory. Franco on the other hand decided to end the operational independence of the Italian forces.