July 6 The first attacks started already during the night of July 5/6, with Republican forces in the cover of darkness penetrating deep into the thinly held Nationalist lines. At daybreak on July 6, the Republicans
bombarded the Nationalist positions using artillery and air power, plus targets in the rear, including the local Nationalist HQ at Navalcarnero. Immediately after the bombardment, the Republican 11th Division commanded by Líster advanced and
encircled Brunete. The Nationalist forces there were completely taken by surprise, and it wasn't until the morning attacks started that they realised the full extent of the Republican operation. Brunete fell to the Republicans by noon. The Nationalists placed overall command of the battle in General Varela. During the morning all available manpower was rushed into the faltering front line, these included personnel from local staffs, field hospitals and supply units, and by noon the 12th, 13th and 150th Divisions along with parts of the
Condor Legion were on their way to help bolster the defense. Later that day the Republican attacks by the 34th and the 46th Divisions on the flanks of Líster's 11th Division stalled upon meeting fierce resistance by the Nationalists and forced Líster to halt his advance south of Brunete. Attempts by the Republican forces to widen the gap by attacking towards the west was also stopped, in front of
Quijorna. The assault on Quijorna was then reinforced by tanks and given the support of both artillery and air assets, but the attackers were again repulsed. Thus far the offensive had almost exclusively been carried out by the V Army Corps. The Republican command seems to have been surprised by their initial success, and there was obviously some confusion which meant that the deployment of XVIII Army Corps was delayed. (This confusion was probably compounded by the fact that many non-communists and regular army officers were reported to be sceptical towards the whole enterprise, which probably made them over-cautious.) The planned east-wing of the enveloping attack, from Carabanchel south of Madrid, never broke the enemy line, despite heavy artillery bombardment.
July 7 The Republican Colonel Jurado diverted the 15th Division to end the stalemate at
Villanueva de la Cañada and the British Battalion of the XVth Brigade managed to clear the village of Nationalists by 7 am on July 7. The Nationalists in the nearby villages of
Villanueva del Pardillo and Villafranca del Castillo continued to hold out. To allow Gal's 15th Division to continue towards Boadilla on the Republican left flank, the 10th Division under Enciso attacked Asensio's 12th Division defending the Mocha Ridge. The Nationalist troops there were driven back and they fell back to the hills near Boadilla. Outside Brunete the day was spent in inconclusive and incoherent fights. The bombardments in the dry landscape, that was parched by the heat, resulted in many wildfires. The Republican insistence on reducing pockets of resistance, rather than bypassing them, gave the Nationalists time to bring up fresh reserves. On the afternoon Nationalist aircraft shifted from the Northern Front started to arrive, and they immediately went into action. Varela was also told that all attacks up north had been suspended, to allow ground units to be rushed to the Brunete sector.
July 8–9 During the night of the 7/8 July general Miaja committed his reserve, the XVIII Army Corps, in an attack towards the east, in the direction of the
Guadarrama River. It was performed in the morning hours. After crossing the river the 15th Division assaulted the newly fortified positions held by the 12th Division for two days. All of the attacks were repulsed and when an attack did succeed in evicting the Nationalist defenders, a
counterattack quickly eliminated the gains made by the Republicans. Meanwhile, the nationalist position at the village of Quijorna on the Republican right flank continued to hold out. The attack south of Madrid was renewed, but failed once again. Nothing more came of this part of the plan. With the Republican attack on the right flank of Líster remaining held up at Quijorna, Modesto ordered the 35th Division to assist ''El Campesino's'' 46th Division. The original intent of the 35th Division was for it to be used in support of Líster's attack through the center. Without the 35th Division, Líster's 11th Division would be unable to advance any further. On the morning of July 9, two Republican brigades attacked at Quijorna, and, after taking heavy casualties, they were able to finally clear the village of Nationalist defenders. On the Republican left flank attacks towards
Boadilla del Monte initially made progress, but even though the assaulting units were well supported by tanks, armoured cars and aircraft their losses were so high that the attacks stranded. The fighting continued though, especially on and around the so-called Mosquito ridge in front of the village. In the first attack the
Spanish Republican Air Force was very active, attacking both ground targets and rebel-held airfields. But the Republican planes were slow and obsolete, which would assure the German
Legion Condor almost total control of the air as the battle would unfold.
July 10–11 On July 10 Villanueva del Pardillo was taken by the XIIth International Brigade of Durán's 69th Division, supported by tanks. Some 500 defenders with weapons, ammunition and material were captured. Villafranca del Castillo was slowly being surrounded by Enciso's 10th Division and Kléber's 45th Division. Colonel Jurado made plans for an assault on the village on July 11, but he became ill and was replaced with Colonel Casado. Citing poor morale and fatigue, Casado requested to cancel the attack, but General Miaja ordered for the attack to proceed as planned. The Republicans were able to trap the Nationalist garrison in Villafranca del Castillo, forcing General Varela to send the 5th Brigade of Navarre to relieve the pressure. The arrival of the Navarrese tipped the balance in favor of the Nationalists as the Republicans were forced from their positions and fled back across the Guadarrama River. A Nationalist attempt to recapture Villanueva del Pardillo on July 11 failed. The activity in the air was very high, as more and more Nationalist air units were committed to the fight. It was not uncommon to see aircraft in groups of thirty or more appear over the battlefield, and clash with equally big squadrons of opponents.
July 12–17 As large Nationalist ground and air reinforcements had arrived to the threatened front, and as the planned pincer movement from the Carabanchel area south of Madrid had failed to make any impression, the Republican offensive was clearly grinding to a halt. Some minor diversionary attacks were still performed, but on July 15 general Miaja finally ordered an end to the offensive. (Major
George Nathan, a battalion commander in the
XV International Brigade, was killed by bomb fragments the day after.) At this moment, the Republicans held Brunete and had cut the Extremadura road. And the offensive had indeed relieved the Nationalist pressure on the Basque country, and it had proved to friend and foe that the Republican forces were rapidly increasing in both strength and capacity. At the same time the Nationalists had prevented their forces besieging Madrid from being cut off and with reinforcements having arrived were able to prepare to counterattack. The Republican forces had suffered big losses, not only from the actual fighting, but also due to the extreme heat, which, combined with lack of water, had incapacitated many soldiers. Many brigades had lost between 40–60% of their numbers – killed, wounded, sick and missing – and one brigade (the
XIVth) is said to have lost 80% of their manpower during this week. The exhausted Republicans dug in and waited for the Nationalist counterattack that they knew probably would come. ==Nationalist counterattack==