[3] From February to August 1942, during the World War II in Yugoslavia, Armellini was appointed commander of the XVIII Army Corps in the Italian-occupied Dalmatia.

[4] After that, he was transferred to Southern Italy at the head of the IX Army Corps to defend the South-eastern coast.

After the fall of the Fascist regime in Italy on 25 July 1943, King Victor Emmanuel III appointed Armellini to succeed Benito Mussolini as commander of the Voluntary Militia for National Security (MVSN), the paramilitary wing of the National Fascist Party (PNF).

From January to March 1944, when Giuseppe Cordero Lanza di Montezemolo was arrested, Armellini assumed the role of head of the Fronte militare clandestino of the Roman Resistance within the Italian resistance movement, later replaced by Roberto Bencivenga [it].

After the World War II, Armellini was president of the Superior Council of the Italian Armed Forces.