Battalion headquarters was established in a sunken cart road running at right angles to the San Martin de la Vega road. No. 2 Company with the machine-gun section was under the command of Harry Fry, who placed his men some fifty yards in front. No. 1 Company moved to the right, taking up positions on what came to be called Conical Hill. On the left, Companies 3 and 4 moved around White House Hill, but soon faced withering fire from the Moors and were forced to fall back to its comparative protection. In a few hours White House Hill would be renamed Suicide Hill.

The Franco-Belge battalion was some 800 long yards to the right of the British, positioned across the San Martin de la Vega road. The British left flank, amazingly, remained open." But nothing could detract from these first moments. One volunteer remembered, "We looked magnificent, we felt magnificent, and we thought that if only our colleagues back home, who had made it possible for us to be there, could see us now, how proud they would be that we had started to repay them for their efforts." The repayment would be in blood unimaginable. The fighting was so intense that the Moors came within thirty yards of the British lines. One volunteer remembered that "men lifting their heads to fire were shot through the face." On seeing his first casualties, another said, "Everywhere men are lying. Men with a curious ruffled look, like a dead bird."

At about 5.30, the men of the Machine-Gun Company, still lying in the trenches, heard during a lull in the firing the singing of the Internationale and saw a body of men advancing towards their positions, giving the anti-fascist salute and shouting: "Vivan las Brigadas Internacionales". At that distance and because of the similarity of dress, our comrades mistook them for the Spanish Battalion. Some thought it was a mass desertion from the fascist lines. Our comrades held up their fists in welcome to the men who were coming over. When they were about 30 metres from the Machine-Gun Company's positions, Company Commander Fry recognised them as fascists by their Mauser rifles and the dress of their officers. So he immediately gave the order to load and fire. Hand to hand fighting took place. Many died in the fascist ranks. The Company lost 10. Comrades machine-gunners, Doran and his crew Jasper Philies and Plum were blown up by grenades while operating their machine-guns. Katscoronas, veteran of four revolutions, ammunition gone, died cracking skulls with his rifle butt.

This story has become part of the legend of the battle of Jarama, though doubts must remain about this version of events. That even the relatively inexperienced British volunteers could confuse conspicuous Moorish troops with Republican soldiers seems unlikely, particularly as the Moors had been their main adversaries the previous day. But as Donald Renton, who was the Machine-Gun Company's political commissar and one of those captured that day, explains, the situation was very confusing with various contradictory instructions being given: "There were different voices raised, you know, to keep firing. Others were for cease fire - "These are our own comrades."

Nevertheless, there is an alternative, and more convincing, version, which originates with George Leeson, a section commander in the Machine-Gun Company, another of the volunteers captured that day. Leeson states that the troops that infiltrated Fry's Machine-Gun Company were members of the Spanish Foreign Legion who had replaced the North African troops. Leeson believed that Fry mistook the advancing Nationalist soldiers for deserters and stood up and told his company to cease fire.

My husband went to Spain because he realized the danger of Fascism, and believed that his military experience could best be used in fighting it. He joined the International Brigade because he thought it was the job he could do best. His experience of Fascist methods of warfare and the brutal treatment of prisoners behind the lines only helped to strengthen his determination to carry on the fight until Franco, Hitler and Mussolini were beaten. This is why he went back to Spain again after a short period of leave, his wound hardly healed, and without even seeing his baby boy which was born the day after he left. I would not has [sic] stopped him even if I could, because I believed he was right, and I am sure that his last thoughts must have been of regret that he could not live to see the final triumph of the forces he fought for. Please excuse me comrade, if I don't write any more."