After proving itself in tests in muddy fields around Rome, the P4 took part in different competitions and demonstrations in the 1920s, many of which were attended by the royal family of the House of Savoy and Benito Mussolini.

In 1923 a modified, militarized version (the Modello 25) won a competition organized by the Ministero della guerra [it] for a heavy artillery tractor.

1,000 units (over a period of four years) of the improved version, the Modello 26, were produced by Fiat (as the Pavesi company was unable to meet the demand) for towing artillery pieces.

Weiss Manfréd Acél és Fémművek in Hungary manufactured a licensed version of the P4, and in 1935 Greece purchased 224 of the tractors from FIAT, which were used to tow Schneidere 105mm and 150mm howitzers.

Sweden licensed the P4 as the Kanontraktor m/28, built by NOHAB Industri AB in Trollhättan, and the German Wehrmacht made use of the tractors starting in September, 1939.