The Clandestine Military Front of the Resistance (FMCR) was set up just a few days after the armistice by colonel Giuseppe Cordero Lanza di Montezemolo, and represented a continuation of the Royal Army: on 23 September 1943, after the Germans occupied the Ministry of War and captured general Calvi di Bergolo, Montezemolo, dressed in civilian clothes, managed to escape and, with soldiers loyal to the Crown, he organised the underground struggle against the occupying forces. He established a radio link with the government of the South, to which he sent daily messages with detailed information about the size and movements of enemy forces.
The objective of the FMCR with regard to the civilian population was to defend it from the violence of the occupiers. It repeatedly sent messages to the Allies deploring the bombings that were harming civilians and giving added force to Nazi-fascist propaganda. To defend the capital, he prepared filters to purify the water of the river Tiber in order to prevent damage from possible destruction of aqueducts by the Germans when abandoning the city, and drew up an emergency plan for the city's power needs. On 12 December the FMCR managed to take watermarked paper from the Italian State Mint and print fake ration cards, to be handed out to the population. About half a million such cards were printed. Another activity was organising anti-sabotage teams in the power plants at Terni and Tivoli.
The Resistance suffered a strong blow when many members of the FMCR were captured: on 23 January generals Simone Simoni and Sabato Martelli Castaldi, major Ugo De Carolis, captain Raffaele Aversa, colonel Giovanni Frignani; on 25 January colonel Giuseppe Montezemolo, in February general Vito Artale. They were all murdered at the Fosse Ardeatine.
Following Montezemolo's arrest general Quirino Armellini took over. At the initiative of the Badoglio government, Armellini succeeded general Roberto Bencivenga at the end of March.