In 1939, the Regia Aeronautica (Italian Air Force) initiated its R Plan, or 3,000 airplanes, a campaign to quickly increase its strength with modern aircraft.

By that time, Regia Aeronautica had been involved in wars on two continents, and its equipment had been depleted and had not kept up with technological advances.

Regia Aeronautica requested Zappata's proposal be modified to incorporate greater strength: the design ultimate load factor was to be increased from 7.0 to 10.0.

Zappata determined that such a change would require significant re-engineering and increased weight, and countered with a proposal for a new two-engine aircraft, the Z.1018.

Thus its performance would be comparable to the proposed Z.1015 with simpler construction, possible lower weight, and reduced maintenance.

Zappata proposed three variants of the basic aircraft, using different wing planforms: The new design also offered the possibility of carrying an internal torpedo, which would have been impossible with the Z.1015 fuselage layout.

The aircraft, in its definitive form (as the Leone I) was a two-engine medium bomber, with a single tail, retractable undercarriage, and metallic structure.

This calculated Z.1018 payload was barely enough for takeoff with full fuel and crew (2,800 kg/6,1703 lb), so it would not allow for any weapon load.

The upper turret was troublesome to install, and was finally mounted in a partially retracted position, which prevented a full field of fire.

In addition, in retrospect the inclusion of a fixed forward-firing gun on a fast bomber appears to have been unnecessary.

The program was well behind the original schedule at that point; Regia had planned on placing the first 32 machines of the type in service by the end of 1939.

The verdict of Mantelli was not encouraging: the 'future bomber' Leone was not enough of an improvement to justify its replacing the CANT Z.1007, which was already in production for Regia Aereonautica.

A measure of the delays which this program suffered is given by the fact that, in spite of pressures caused by the war being waged at that time, it had taken six months to complete the proof-of-concept aircraft, and a true prototype would still have to be constructed in order to verify the adequacy of the basic design.

This mixed construction required additional considerations to be made, since wood and metal structures have very different properties and are thus difficult to integrate into a single airframe.

In addition to this metal-to-wood conversion challenge, the continual government requests for modifications and improvements slowed production.

The two-year program delay meant that the pre-series aircraft were competing with upgraded versions of the CANT Z.1007, the "Ter".

The first wooden example was tested for almost all of 1942, reaching a level speed 524 km/h (326 mph) despite the much heavier weight, mainly because of its improved aerodynamics.

Due to the 2,013 kW (2,700 hp) installed power, it reached 6,000 m (19,690 ft) altitude in 14 minutes 4 seconds (lightly loaded).

In flight, the aircraft was quite stable, but vibrations occurred at high speed in turbulence, and control response was considered sluggish.

Also, the first series example was affected by several problems of tail vibration and even poorer control response.

This was a great improvement compared to the early Italian fighters, but this was a big and heavy aircraft, a medium bomber, so the space and payload was not a problem, just as with the German Dornier Do 217, one of the similar aircraft developed in the rest of the world, and which had been sent to Regia Aereonautica in small numbers.

After a brief evaluation in a squadron, MM.24824 was caught by surprise by the armistice in CRDA and captured by Germans, but was not employed and did not survive the war.

The aircraft showed itself as fully capable to perform this task but the two examples were not employed (the other was damaged by an accident on the ground).

During this time, Zappata noted that CRDA was saturated with production of all his projects, so he moved to Breda, which was idle after the failure of its Ba.88.

Breda was in similar condition, with the assembly lines destroyed on 30 April 1944 by aerial bombing and also in this occasion Germans ordered the demolition of all the hardware.

All in all, the CANT Z.1018 Leone was an overall an improvement over the CANT Z.1007, mainly thanks to the two-engine configuration, but the program was hampered by continuous alteration requests made by Regia Aeronautica.

The small Italian industrial base, and the quick decay of the military effort, made the situation even worse.

This modest amount was the only result of the programs made by Regia Aeronautica to upgrade her bomber fleet.