After the Kingdom of Italy entered World War I on 24 May 1915 he arrived enlisted in the Royal Italian Army with the rank of second lieutenant, reaching the front on 17 August.

On 3 June 1916, while serving in the 212th Infantry Regiment "Pescara", he was captured on Monte Cengio during the battle of Asiago; he spent the rest of the war in captivity, finally returning to Italy on 26 November 1918.

After the outbreak of the Spanish Civil War he volunteered again and was given command of the 1st Battalion "Sierra Avila" of the 1st "Blue Arrows" Regiment of the Flechas Azules Division.

[1][5][6] After the Italy's entry in the Second World War Mittica was recalled into service with the MVSN and given command of the 45th Assault Blackshirt Legion "Alto Adige", landing in Durrës on 30 December 1940.

On 6 June 1942 he returned once again to the front, replacing Niccolò Nicchiarelli at the head of the 63rd Assault Blackshirt Legion "Tagliamento", fighting on the Eastern Front as part of the 8th Army, being awarded his third War Cross for military valor and fourth silver medal for military valor, as well as the German Iron Cross second class, for having repelled a Soviet offensive on the Don river in September 1942.

In early 1944 Benito Mussolini chose him as one of the judges in the Verona Trial against six members of the Grand Council of Fascism who, in the session of 25 July 1943, had voted a motion of no confidence against the Duce, causing his resignation and the fall of the regime.