On February 14, 1937 he volunteered for the Spanish Civil War as an officer of the Voluntary Militia for National Security (MVSN), participating in the early stages of the Battle of Bilbao, although at the time of the fall of the city he was on leave.

[1] In 1940, after the beginning of the Second World War, he was recalled into service as a reserve artillery officer in the Royal Italian Army, while continuing to write newspaper articles and essays on geopolitics.

[2][3] After the Armistice of Cassibile, Solaro joined the Italian Social Republic, and on 16 September 1943 he was appointed to lead the Republican Fascist Party (PFR) of Turin, governing in a triumvirate along with Luigi Riva and Blackshirt General Domenico Mittica.

The collapse of the Italian Social Republic was however imminent, and the city's military leaders, headed by General Enrico Adami Rossi, decided to leave Turin and retreat towards the Valtellina, while Solaro tried in vain to persuade them to stay.

Finding it closed, he went instead to the Cassa di Risparmio where, having obtained a refusal from the director, he broke down the gate with an armored vehicle and withdrew seventeen and a half million lire.

He refused to join the departing ENR column and hid in the cellars of the local agricultural consortium with three of his followers, but in the morning of 28 April they were discovered and captured by a partisan squad.