After the diesel engine failed to impress, the Italian Army settled on a gasoline-fueled version, forcing Ansaldo engineers back to the development board which served to delay the program. This endeavor eventually produced a gasoline-fueled engine outputting at 420 horsepower. The new tank was now designated as the "P 40" and it was in this end form that the type survived prior to the Italian Armistice. From then on, the tank would be known under the formal designation of "P 26/40" - "26" marking the vehicle's weight in tonnes while "40" denoting its year of adoption into service.
Primary manufacture of the P 26/40 was conducted out of the Ansaldo facility in Northern Italy - even after the Italian Armistice. The vehicle maintained a running length of 19 feet with a width of 9 feet, 2 inches and a height of 8 feet, 2 inches. She was crewed by four personnel that included the driver, the tank commander, the ammunition handler and a radio-operator/machine gunner. Key to this arrangement was the commander for he also doubled as the gun layer which complicated in-the-field actions. Comparable tank systems from other nations incorporated a fifth crewmember to serve as a dedicated gunner while the commander could concentrate on communicating with his crew and observing (and reacting to) battlefield developments - where seconds could spell victory or total doom for the crew. Additionally, the P 26/40 was designed with only a two-man turret system which also limited internal space - three-man turrets were now proving the norm with all new tank designs appearing elsewhere. Not only was the workload of the commander doubled in the Italian design but creature comforts were few and far between. Couple the space required for each work station with the available ammunition stores, engine compartment and transmission "hump" running along the hull floor and one can imagine the rather tight confines of the Italian design. There was no commander's cupola to provide the vehicle commander with a perched position from which to observe actions from afar which proved another tactical limitation in-the-field.
Armor protection for the P 26/40 varied about her design, ranging from 14mm at her thinnest to 60mm at her thickest facings. While something of an improvement over preceding Italian tank designs, this was rather woeful when compared to the anti-tank weaponry being fielded by Italy's enemies. Any anti-tank gun larger than 40mm was said to be able to penetrate the base armor of the P 26/40 with relative ease at this point in the war. To compound issues in the Italian design, the armor was finished in riveted construction as opposed to the much more accepted welded construction appearing on tanks elsewhere. Not only was riveted construction weaker along the plate joints (regardless of actual plate thickness), the rivets themselves could fly about the fighting compartment in response to a direct hit from enemy fire - injuring or outright killing the crew within.
Primary armament of the final P 26/40 form was a single Ansaldo-brand 75mm L/34 series main gun fitted to the traversing turret. This was backed by one 8mm Breda machine gun fitted coaxially in the turret intended for infantry defense. Some 65 projectiles of 75mm ammunition were stored aboard the tank as were 600 rounds of 8mm ammunition.
Production quality P 26/40s were powered by a single V-12 SPA 342 series diesel engine of 420 horsepower. This supplied the machine with a top road speed of 25 miles per hour (16 miles per hour off road) with an operational range of approximately 170 miles. The design was tied to a semi-elliptical leaf spring bogie suspension that allowed such values but this arrangement suffered much in terms of speed when off road compared to her contemporaries abroad.
Much had changed since design work on the P 26/40 had begun. Principally, the arrival of the Soviet T-34 Medium Tank ushered in a new era of tank design in which thick, sloped armor was the call of the day. Its success against the German lines prompted the Italians to rewrite their tank "wish list" to an extent, forcing a redesign of their P 26/40 to bring about more sloped, thick armor facings for basic ballistics protection. The design changes naturally affected the vehicle's intended weight and operating scope - now charged in the latter with engaging enemy armor head-on as opposed to supporting infantry or medium tank maneuvers. The Italian Army ordered some 1,200 P 26/40 tanks for its inventory - quite optimistic for Italian war time industry and a total that would never be met by war's end.
With the P 26/40 design in check, attention was given to evolving the existing design and chassis for other battlefield forms. The "P 43" was intended as an "up-armored" form of the base P 26/40, fielding as much as 80mm of armor thickness to contend with the growing use of anti-tank weaponry on the World War 2 battlefields. Armament considered was a 90mm main gun or a long-barreled 75mm form. The P 43bis was intended to take on a more powerful, gasoline-fueled 480 horsepower engine. At any rate, these design initiatives did not proceed past the mock-up stage before the Italian surrender.
A more promising endeavor was the "Semovente 149/40" beginning life in 1942 as a dedicated self-propelled gunnery platform intended for mobile, long-range fire support. The type was to be armed with a formidable 149mm artillery-based gun barrel in place of the turret and superstructure, consistent with Italian SPG designs of the war. However, like other P 26/40 initiatives, the Semovente 149/40 fell to naught - done in by a deteriorating war situation within Italy and lackluster trials of the single prototype completed. This pilot vehicle passed on to the Germans after the Italian surrender and was eventually captured by the Americans, ending her existence in trials at the Aberdeen Proving Grounds of Maryland, USA.
Serial production for the P 26/40 was slated for 1943. However, the Italians surrendered in September of that year, bringing about an end to her Axis support and yielding less than a handful of pre-production tanks (some sources state as many as 20 production-quality vehicles were delivered to the Italian Army). The Germans, still attempting to keep their cause alive in Italy, took over production through Ansaldo which continued into 1944 - yielding approximately 80 to 100 more of the type (under the German Army designation of Panzerkampfwagen P40 737(i)). Lack of engines meant that many were set as fixed defensive gun positions while those completed in whole saw only limited combat against the invading Allies - particularly at the Anzio beachhead. In all, however, the P 26/40 was done in by a myriad of issues - a slow-paced design and development period, a lack of a suitable proven engine from the outset, Italy' s eventual capitulation and a set of outclassed specifications and qualities. Even so, the P 26/40 remained one of the more complete Italian tank designs of the war.