Giovanni Berretta was from Milano.

Berretta served as a volunteered in the Spanish Civil War in the 3^a Escuadrilla de Caza del Tercio.

On the morning on 15 November, 15 CR.32s provided the fighter escort for bombers attacking targets in Madrid. As they neared the city, four I-16s led by Leitenant Sergey Chernykh (Escuadrilla Kolesnikov) attacked the Italian section consisting of Sottotenenti Bernardino Serafini and Giuseppe Cenni and Sergente Berretta. All three pilots ably defended themselves and collectively shot down an I-16 piloted by Vladimir N. Vzorov (’Jose Zoro’), who destroyed his fighter when he crash-landed into an olive grove.
The Russian pilots reported nine I-16s took off to intercept Ju 52/3m bombers, escorted by fighters, heading for Madrid. Leitenant Sergey Denisov (’Ramon’) and Leitenant Chernykh (’Garcia’) each reported downing an enemy fighter.
It is possible that one CR.32 was lost since it was reported that the body of a Nationalist pilot was found at the outskirts of Madrid.

Sergente Maggiore Berretta was decorated with the Medaglia d’argento al valor militare (gazetted 1938) for his actions over Spain between October and December 1936:

"During a perilous mission for which he volunteered, he courageously faced the most challenging trials, consistently demonstrating exemplary valour and a calm spirit of sacrifice."
Skies of Spain, October-December 1936-XV.

Berretta ended the Spanish Civil war with one shared biplane victory.

Claims:

Kill no.	Date	Time	Number	Type	Result	Plane type	Serial no.	Locality	Unit
	1936
	15/11/36	morning	1/3	I-16 (a)	Shared destroyed	Fiat CR.32		Madrid	3a Escuadrilla de Caza del Tercio

Biplane victories: 1 shared destroyed.
TOTAL: 1 shared destroyed.
(a) Claimed in combat with I-16s, which claimed 2 enemy fighters while losing 1 I-16 (pilot safe). The CR.32s claimed 1 I-16 without losses (or possibly 1 lost).

Sources:
Elenco Nominativo dei Militari dell’ A. M. Decorati al V. M. Durante it Periodo 1929 - 1945 1 Volume A - L
Fiat CR.32 Aces of the Spanish Civil War - Alfredo Logoluso, 2010 Osprey Publishing, Oxford, ISBN 978-1-84603-983-6
Giuseppe Cenni, pilota in guerra – Giuseppe Pesce, 2002, USSMA, Rome, kindly provided by Stefano Lazzaro.
Istituto del Nastro Azzurro
Polikarpov I-15, I-16 and I-153 Aces - Mikhail Maslov, 2010 Osprey Publishing, Oxford, ISBN 978-1-84603-981-2
Additional information kindly provided by Stefano Lazzaro, Alfredo Logoluso and Giovanni Massimello.