In 1911 Rojo entered the Infantry Academy at the Alcazar of Toledo, receiving his commission in 1914 with the rank of second lieutenant, fourth in a class of 390 cadets.

In 1922, having risen to the rank of captain, he returned to the Infantry Academy in Toledo, where he occupied diverse educational and administrative positions.

During his time at the academy, a peculiar event took place in which he proposed to the cadets a tactical assumption that consisted of passing through the river Ebro to establish a route in the Reus-Granadella, an operation very similar to one a few years later, during the civil war, he would later put into practice in the famous Battle of the Ebro in the area between Mequinenza and Amposta.

In October 1936 he was promoted to lieutenant colonel and was designated head of the General Staff of the Forces of Defense commanded by General Jose Miaja,[6] head of the Junta de Defensa de Madrid created to defend the capital at all costs after the transfer of the Republican government from Madrid to Valencia.

[13] He was awarded the highest Republican decoration, the "Placa Laureada de Madrid" on 11 January 1938 for his planning of the last mentioned operation.

After a brief stay in that country, the Service of Emigration of Spanish Republicans (SERE) paid his passage to Buenos Aires.

Although he was not bothered in the beginning by the Francoist authorities,[citation needed] on 16 July 1957 the Special Court for the Repression of Masonry and Communism informed him that he would be prosecuted for the crime of military rebellion, in his position as ex-commander of the Army.

Franco held Rojo in such high esteem that he granted him the pension due a Lt. General of the Spanish army upon his return to Spain.

[citation needed] He wrote several books detailing his military experiences in the civil war, which were published in the following order: ¡Alerta a los pueblos!