The small 34-year-old played a key role in the February 1937 Battle of Jarama. He was wounded after leading the January 1937 battle at Los Rozas and in order to fight at Jarama it is reported that he "left hospital with a fever to go and fight". The battle at Jarama was one of the principal actions of the Spanish Civil War. If the Jarama valley were surrendered, the road from Madrid to Valencia would be cut off allowing Madrid to be taken by the Fascists which for all intents and purposes would cost the Spanish government the war. Along with Frank Ryan he rallied the remnants of the British Battalion in a defensive action which held the line outside Madrid. Cunningham led a bombing raid down a trench held at one end by the Fascists and at the other end by the Spanish government troops. They took this trench and with six men and a Lewis gun, cut off a group of some 80 Fascists from their own lines. This almost impossible defence blocked Franco's attempt to seize the capital. The Jarama action had left him with three rifle wounds through his left upper arm and another rifle bullet under his shoulder blade that had entered his left chest, passed through, and lodged there. Cunningham was hospitalised from 15 March 1937.