The Caproni Ca.135 was an Italian medium bomber designed in Bergamo in Italy by Cesare Pallavicino. It flew for the first time in 1936, and entered service with the Peruvian Air Force in 1937, and with the Regia Aeronautica (Italian Royal Air Force) in January 1938.
Origins
General Valle (Chief of Staff of the Regia Aeronautica) initiated the "R-plan" – a program designed to modernize Italy's air force, and to give it a strength of 3,000 aircraft by 1940. In late 1934 a competition was held for a bomber with the following specifications: Speed: at and at . Rate of climb: in minutes. Range: with a bombload. Ceiling: . The ceiling and range specifications were not met, but the speed was exceeded by almost all the machines entered. At the end of the competition, the "winners" were the Ca.135 (with 204 aircraft ordered), the Fiat BR.20 (204), the Savoia-Marchetti SM.79 (96), the CANT Z.1007 (49), and the Piaggio P.32 (12).
This array of aircraft was proof of the anarchy, clientelism, and inefficiency that afflicted the Italian aviation industry. Worse was the continuous waste of resources by the Regia Aeronautica (Italian Royal Air Force). Orders were given for aircraft that were already obsolete. The winners of the competition were not always the best – the BR.20 was overlooked in favour of the SM.79, an aircraft which was not even entered in the competition.
Design The Ca.135 was to be built at Caproni's main Taliedo factory in Milan, which is why the type had a designation in the main Caproni sequence, rather than in the Caproni-Bergamaschi Ca.300 series. However, the project was retained at Ponte San Pietro and the prototype, completed during 1934–35 (a long construction time for the period), was first flown on 1 April. The project chief was Cesare Pallavicino of CAB (Caproni Aereonautica Bergamasca).
Although the new bomber was in the "century series" of Caproni aircraft, it resembled the Caproni Ca.310, with its rounded nose, two engines, low-slung fuselage and wings with a very long chord. Several versions were fitted with different engines and some had noticeable performance differences.
The prototype was powered by two (at ) Isotta Fraschini Asso XI.RC V12 engines initially fitted with two bladed wooden propellers. It had a length of , a wingspan of , and a wing surface of . It weighed empty and had a useful load. Structurally, it was built of mixed materials, with a stressed-skin forward fuselage and a wood and fabric-covered steel-tube rear section; the wings being of metal and wood, using fabric and wood as a covering. The wings were more than of the total length, and had two spars of wooden construction, covered with plywood and metal. The strength coefficient was 7.5. The tail surfaces were built of wood covered with metal and plywood. The fuel system, with two tanks in the inner wings, held a total of 2,200 L (581 US gal).
The Ca.135's fuselage shape was quite different from, for example, that of the Fiat BR.20. If the latter resembled the American B-25 Mitchell, the Ca.135, with its low fuselage more resembled the American Martin B-26 Marauder. Its long nose accommodated the bomb-aimer (bombardier) and a front turret (similar to the Piaggio P.108 and later British bombers). The front part of the nose was detachable to allow a quick exit from the aircraft. It also had two doors in the cockpit roof, giving the pilots the chance to escape in an emergency. The right-hand seat could fold up to assist entry to the nose.
A single 12.7 mm (0.5 in) in a turret in mid-fuselage, was manned by the co-pilot. A seat for the flight engineer was later fitted. The wireless operator's station, in the aft fuselage, was fitted with the AR350/AR5 (the standard for Italian bombers), a radiogoniometer (P63N), an OMI AGR.90 photographic-planimetric machine or the similar AGR 61. The aircraft was also equipped with an APR 3 camera which although not fixed, was normally operated through a small window. The wireless operator also had a 12.7 mm (0.5 in) machine gun in the ventral position. All this equipment made him very busy; as a result, an extra man was often carried. The aircraft had very wide glazed surfaces in the nose, cockpit, and the central and aft fuselage; much more than in other Italian aircraft.
The aircraft was fitted with three machine guns: two 12.7 mm (0.5 in) calibre in the upper turret rsp. belly-stand and one 7.7 mm (0.303 in) calibre gun in the nose. All had 500 rounds, except the 7.7 mm (0.303 in) which had 350.
Bombload, like most Italian bombers, was less than impressive in terms of total weight, but was relatively flexible, depending on the role – from anti-ship to close air support: 2 × bombs (the heaviest in the Regia Aeronautica), plus 2 × , and 2 × , for a total of 2 × + 4 × + 2 × , total nominal 4 × 8 × + 8 × + 4 × , total 16 × + 8 × , total 24 × , , , or . 120 × bomblets 2 × torpedoes (never used, but hardpoints were fitted) The aircraft had a better bomb capacity than most of its contemporaries (the SM.79 could carry: 2 × 500 kg/1,100 , 5 × , 12 × bombs, or 700 × bomblets).
Performance The aircraft was underpowered, with a maximum speed of at and a high minimum speed of , (there were no slats, and maybe not even flaps). Ceiling was only and the endurance, at 70% of throttle, was . All-up weight was too high, with total of , not as expected.
The total payload of was shared between the crew (320+ kg/705+ lb), weapons (), radios and other equipment (), fuel (2,200 L/581 US gal), oil (), oxygen and bombs. There was almost no chance of carrying a full load of fuel with the maximum bombload, (other Italian bombers were generally capable of a payload). The lack of power made take-offs when over-loaded, impossible. Indeed, even with a normal load, take-offs were problematic.
Take-off and landing distances were . The range was good enough to assure with and with .
The production version was fitted with two inline liquid-cooled Asso XI RC.40 engines, each giving at . Aerodynamic drag was reduced, with three-bladed metal propellers that were theoretically more efficient. These new engines gave the aircraft a maximum speed of at . It could climb to in 5.5 minutes, in 12.1 minutes and in 16.9 minutes.
Despite this, the aircraft was still underpowered, so in 1939 the already built Ca.135 "Asso" were refitted with Piaggio P.XI engines, taking the name of Ca.135 Mod.
Operational service The aircraft arrived late in respect to the others (like the BR.20), and with totally unsatisfactory technology. Despite this there was an order for 32 aircraft from the Regia Aeronautica on 19 June 1937. They started to enter service in January 1938, over a year after the BR and SM bombers.
Spanish Civil War In 1938 eight aircraft were earmarked for the Aviazione Legionaria to serve in the Spanish Civil War. These Tipo Spagna ("Spanish Type") aircraft were refitted with Fiat A.80 R.C.41 engines, rated at .
Crews from 11 Wing were sent to Taliedo (just outside Milan), to take the first seven aircraft – designated Ca.135S – to Spain. One was damaged on take-off, the other six flew to Ciampino near Rome, where two suffered damage on landing. After repairs and some modifications, the seven aircraft were not ready to leave for Spain until late 1938. During the flight two were forced by icing to return to Italy and three crashed into the sea. Only two arrived at Palma de Mallorca, where they remained unused for six months.
Italy Production of the aircraft was initially 32 aircraft, of which eight were modified in Ca.135 Ss, the others were modified into the Ca.135 Mod. The first Ca.135 Bis were built in 1938. They were fitted with Piaggio P.XI RC.40 engines, with Piaggio P.1001 three-blade metal propellers. Length was , wingspan , and wing surface 60 m (646 ft). Armament was still only two 12.7 mm (0.5 in) guns and one 7.7 mm (0.303 in), but the nose was redesigned to be more aerodynamic. Another 32 aircraft were ordered and built between 1939 and June 1940.
They were not successful aircraft, being heavily criticized by the Italian pilots. Unable to be used operationally, they were sent to flying schools, and then exported to Hungary. The first batch of Ca.135s flown by 11 Wing were phased out by late 1938. 25 were still available at Jesi airfield, but only four were airworthy. The others were probably in maintenance for engine replacement. There were at least 15 Ca.135Ss and Ca.135Mods at the Malpensa flying school in 1940, the poor condition of these aircraft meant that they were scrapped in November 1941. With the scrapping of the first batch and the selling of the second, all 64 Ca.135s left the service of the Regia Aeronautica without performing a single operational mission.
Hungary
The Magyar Királyi Honvéd Légierő (MKHL; the Royal Hungarian Air Force) ordered Ca.135s which were delivered in 1940 and 1942 in two series of 36 resp. 31 (originally 32, but one plane was lost on the delivery flight) planes. Also a licence production of aircraft and engines was considered.
The Hungarians operated a total of 67 Ca.135bis with some success against the Soviet Union on the Eastern Front in 1941 and 1942, once Hungary had committed its forces in that sector during World War II.
These aircraft constituted almost the entire Hungarian heavy bomber force. They were ordered after Hungarians returned 33 out of 36 Caproni Ca.310s acquired between May and September 1939. Because of an Italian credit for 300 million lire and the impossibility of acquiring modern German aircraft, the Hungarian Air Force acquired the new, more powerful, Ca.135bis. They were ordered in Dec 1939.Neulen 2000, p. 121. After that "deal" the first charge was delivered in May/June 1940, the second one in May 1942 (from a second order submitted in July 1941). Regia Aeronautica had rejected the Ca.135s on account of its technical shortcomings and the aircraft had been taken off production. But in Hungarian service this bomber proved quite satisfactory.Neulen 2000, p. 121.
When Hungary declared war on the Soviet Union in June 1941, the Hungarian Air Force was almost entirely equipped with Italian aircraft.Neulen 2000, p. 121. The bombers had their baptism of fire on 27 June 1941, the day Hungary declared war. That day, 1st Lt Istvan Szakonyi, in his Ca.135 from the 4/III Bomber Group, managed to destroy an important bridge with a 'trial drop' of two bombs.Neulen 2000, p. 124. The Ca.135s equipped the 3./III Group of 3rd Bomber Wing, based in Debrecen, a bomber unit of the Hungarian air formation commanded by Lt Col Béla Orosz, that had been tasked to provide air support to the Hungarian Rapid Corps, subordinated to the German 17th Army.Neulen 2000, pp. 124–125.
On 11 August, six Capronis, commanded by 1st Lt Szakonyi, took off to bomb a 2 km (6,560 ft) bridge across the Bug River of the city of Nikolayev, on the Black Sea. One Ca.135 had to turn back due to engine problems, but the other five, escorted by Hungarian Fiat CR.42s and MÁVAG Héja Is, continued eastwards. Szakonyi's Caproni was hit by AA fire and lost his port engine but the squadron commander remained in action. One of his pilots, Capt. Eszenyi, destroyed the bridge, and Szakonyi bombed the Nikolayev train station. On the way back the Capronis were intercepted by Soviet Polikarpov I-16 fighters. The escorting Hungarian fighters shot down five I-16s, while Szakonyi's crippled Ca.135 managed to destroy another three Polikarpovs. After the German 11th Army captured Nikolayev, on 16 August, the commander of Luftflotte 4, Col Gen Lohr, decorated the successful Hungarian crews at Sutyska.Neulen 2000, pp. 125–126.
The Ca.135 on the Eastern Front had frequent malfunctions and its insufficient combat load-carrying capability set high demands on the mechanics maintaining it. A 50% operational readiness of the Capronis was to be seen as a great achievement.Neulen 2000, p. 121.