Battle of Jarama The Battle of Jarama ( February 6 – 27 , 1937 ) was an attempt by General Franco ' s Nationalists to dislodge the Republican lines along the river Jarama , just east of Madrid , during the Spanish Civil War . Elite Spanish Legion naires and Moroccan " Regulares " from the Army of Africa forced back the Republican Army of the Centre , including the International Brigades , but after days of fierce fighting no breakthrough was achieved . Republican counterattacks along the captured ground likewise failed , resulting in heavy casualties to both sides : Preliminaries . By winter of 1937 the Nationalist forces , led by Francisco Franco , having failed to carry Madrid by storm in November 1936 , resolved to cut off the city by crossing the Jarama to the south east and severing Madrid ' s communications with the " pro tempore " Republican capital of Valencia . General Mola was in overall command of the Nationalist forces around Madrid and planned an offensive across the Jarama 11 km south of the capital . General Orgaz was put in command of the front , with General Varela exercising command in the field . The attack had been intended to coincide with an offensive by Franco ' s Italian allies under General Mario Roatta at Guadalajara , but the Italians were not ready in time and Mola decided to press ahead without them . The Nationalists had roughly 25 , 000 infantry , mostly " regulares " and Spanish Foreign Legion naires . Mola also had ten squadrons of cavalry at his disposal . They were supported by German troops from the Condor Legion , including two heavy machine gun battalions , a tank corps under Wilhelm Ritter von Thoma and batteries of 155mm and 88mm guns . The initial objectives of the Nationalists were to take the western bank of the river Jarama and to capture the heights that overlooked it . Next , they would break through the Republican positions on the high ground east of the river and take the towns of Vaciamadrid and Arganda in order to sever the Madrid — Valencia road and cut off the capital to the south and east . Taking the west bank . The Nationalist offensive began on February 5 with assaults on the Republican positions on the west bank of the Jarama . The opening attacks took the Republicans by surprise . The Nationalists , as was the fashion of the Army of Africa , advanced in mobile columns and overwhelmed the unprepared Republicans . General García Escámez commanded their right flank ( to the south ) , General Rada commanded the left , or northern wing , while General Asensio commanded the centre . Escámez attacked on February 6 at Ciempozuelos and overran the Republican forces which lost 1 , 800 men . Rada ' s men took La Marañosa hill , 700 metres high , which overlooked both banks of the Jarama . The two Republican battalions atop " La Marañosa " vainly stuck to their cliff - top defences and died there to the last . From this hill - top position , the Nationalists could dominate the river crossing with artillery and machine gun fire . By February 8 , the west bank of the Jarama was in Nationalist hands . Elements of General Pozas ' Army of the Centre had already begun taking flight when Líster and " El Campesino " showed up with their veteran brigades on February 8 and stabilized the line . Reinforcements appeared on the east bank of the Jarama and the Republic ' s army reorganized its defences , forestalling any enemy crossing . In addition , heavy rain flooded the river and held up fighting for two days . Nationalists cross the river . On February 11 a small group of Moroccan " regulares " crossed the river undetected and crept up to the positions of the Republican XIV International Brigade near the Pindoque railway bridge at Vaciamadrid . As they had learned to do in the Rif War , the " regulares " slipped inside the enemy perimeter and silently cut the throats of the sentries . Nationalist cavalry under Barrón followed them across almost immediately and attacked the fleeing XIV Brigade . Nearby , Barrón ' s column , braving heavy Republican fire , charged across the Arganda bridge and established a bridgehead on the other side . The Republicans had laid demolition charges on the bridge , but although they were detonated , the bridge remained intact . Further south , Asensio attacked the village of San Martín de la Vega , where Republican machine gun ners brought his advance to grief before being silenced by Moroccan and Legionnaire knifework . At this point , Nationalist troops under Varela crossed the river in force . However , the Republicans remained firmly entrenched along the Pingarrón heights on the eastern bank and continued to plaster the Nationalist bridgeheads with artillery fire . Barrón ' s brigade was held up by the Garibaldi Battalion , which held the high ground near Arganda . Late in the day , units of XI International Brigade held off a Nationalist push onto the Arganda — Colmena road . The Republicans then counterattacked twice with Soviet tanks , which were beaten off with artillery fire from Nationalist batteries dug in on " La Marañosa " , but they served to hold up further Nationalist advances . When Junkers of the Condor Legion appeared overhead in support of the Nationalists , Republican planes shot them down and took control of the skies . Until February 13 , the Republican air force , largely composed of Soviet machines and pilots , maintained air supremacy . However , they were challenged by the arrival of more Italian and Spanish nationalist aircraft , with the result that , by the end of the battle , neither side had a decisive advantage in the air . The Nationalists brought their reserves forward and opened on February 12 a powerful attack in the direction of Morata . Asensio ' s troops took the Pingarrón hills and assaulted the Pajares heights to the north . This struggle for the high ground east of the Jarama would see some of the most bitter fighting of the battle . Suicide Hill . The XI International Brigade ( composed of British , Irish , Balkan , French and Belgian volunteers ) defending the Pajares found itself outmanned and outgunned . Nationalist artillery massed on the heights of Pingarrón and pummeled the defenders . The German Thälmann Battalion held off a frontal assault on their hill - top , inflicting severe casualties on the attacking " regulares " with machine gun fire , but the British were forced back and took up position at a place they named " Suicide Hill " . A machine - gun battalion arrived in support but proved of little use , having been issued the wrong ammunition . However , Líster ' s veteran Spaniards appeared to the left of the British and helped the Republican line hold all day and through the night , despite frightful casualties . A furious and confused fight followed in which the British Battalion lost poet Christopher Caudwell and 375 of their 600 men , including almost every officer . On February 13 , Nationalist forces started a flanking manoeuvre and forced back the French units to the right of the British . They were then able to isolate and capture 30 members of the machine gun battalion . The surviving Republicans gave up the hill and retreated to the heights , where the enigmatic , pseudonymous " Colonel Gal " — whose identity was never confirmed with certainty — rallied the officers and convinced them to rejoin the battle . The Nationalists , mistaking the returning Republicans for their own soldiers , gave up the hill to them without a fight before realizing their error and resuming the struggle . By the night of February 14 , fresh troops arrived to shore up the Republican line . The farthest Nationalist advance was made to the south of " Suicide Hill " in the low hills between the heights of Pajares and Pingarrón . There the Nationalist centre made a breakthrough , after the XV International Brigade was smashed by artillery fire from the Nationalist 155mm guns on Marañosa hill . Barrón ' s troops almost reached the town of Arganda del Rey and the coveted Madrid — Valencia road . However , their advance was halted by orders from General Varela , who was concerned that they would be cut off if they advanced too far ahead of other Nationalist units . Republican counterattack . On February 14 , the Republicans counter - attacked Barrón ' s men with 50 T - 26 tanks , supported by infantry , artillery and air cover . Although it did not re - take any lost ground , the counter - attack again bloodied the Nationalists and halted their advance . The shaken Nationalists went as far as to call the 14th " " el día triste del Jarama " " ( " the sad day , " a throwback to Hernán Cortés ' " Noche Triste " ) . On February 17 , General José Miaja took overall command of the Republican front . Command had previously been split between him and General Pozas , hampering the co - ordination of Republican strategy . Miaja mounted a major counter - offensive to clear the eastern back of the Jarama . Forces under Líster made a frontal assault on the heights at Pingarrón , only to be driven back with up to 50 % casualties . On the tactical execution of these counterattacks , one Nationalist soldier reflected : Another futile and costly attack was made by troops under Juan Modesto from the direction of the Manzanares river to the north on the Nationalist hill - top position at Marronosa . Here again , the Republicans failed , at a heavy cost , to achieve their objectives . In the northern sector however , the Nationalists were forced back , away from Vaciamadrid and the Madrid — Valencia road . Further Republican counter - attacks followed between February 23 and February 27 . General Gal ordered another attempt to storm the Nationalist strongpoint at Pingarrón . The Republican forces involved included 450 Americans of the Abraham Lincoln Brigade under Robert Merriman . The inexperienced troops , advancing without artillery support , marched bravely into the teeth of the Nationalist lines and were cut to pieces . Poet Charles Donnelly ( part of an Irish contingent known as the Connolly Column ) was heard to remark , " even the olive s are bleeding " , before being gunned down by a burst of machine gun fire and killed . The Americans lost 120 dead and 175 wounded , or 66 % casualties . After the failure of this attack , the Jarama valley settled again into silence . Both sides dug in and the front stabilised . Aftermath . By the end of February the front lines had stabilized , with both sides consolidating and fortifying their positions to the point where no useful assault could be undertaken . Nationalists and Republicans alike had suffered very heavy losses ( of between 6 , 000 to 25 , 000 each , depending on different estimates ) . In addition , their troops were exhausted and low on ammunition and food . Although the Nationalists succeeded in crossing the river and resisted all efforts to dislodge them from their footholds on the other side , the Madrid — Valencia road remained out of reach and firmly in Republican hands . Consequently , the area lost much of its strategic importance and merged into the wider front , lined with trenches and reminiscent of the static struggle of the First World War ' s Western Front . In March , the Italian Expeditionary Army was likewise thrown back at Guadalajara , ending Franco ' s hopes of cutting off Madrid .