Dassault Mirage IV

The Dassault Mirage IV was a French jet-propelled supersonic strategic bomber and deep-reconnaissance aircraft. Developed by Dassault Aviation, the aircraft entered service with the French Air Force in October 1964. For many years it was a vital part of the nuclear triad of the Force de Frappe, France's nuclear deterrent striking force. The Mirage IV was retired from the nuclear strike role in 1996, and the type was entirely retired from operational service in 2005.

During the 1960s, there were plans of export sales for the Mirage IV; in one proposal, Dassault would have entered a partnership with the British Aircraft Corporation to jointly produce a Mirage IV variant for the Royal Air Force and potentially for other export customers, however this project did not come to fruition. The Mirage IV was ultimately not adopted by any other operators beyond the French Air Force.

Origins
Work on a supersonic bomber able to carry a nuclear bomb started in France in 1956 as part of the development of France's independent nuclear deterrent. In May 1956, the Guy Mollet government drew up a specification for an aerially refuelable supersonic bomber capable of carrying a 3-metric-ton, 5.2-meter-long nuclear bomb 2,000 km (without aerial refuelling). The final specifications, jointly defined by government authorities and Dassault staff, were approved on 20 March 1957. Sud Aviation and Nord Aviation both submitted competing proposals, both based on existing aircraft; Sud Aviation proposed the Super Vautour, a stretched Sud Aviation Vautour with 10,500 lb thrust Atar engines and a combat radius of 1,700 miles at Mach 0.9. Dassault's proposal for what became the Mirage IV was chosen on the basis of lower cost and anticipated simpler development, being based upon a proposed early 1956 twin-engined night-fighter derived from the Dassault Mirage III fighter.

Dassault's resulting prototype, dubbed Mirage IV 01, looked a lot like the Mirage IIIA, even though it had double the wing surface, two engines instead of one, and twice the unladen weight. The Mirage IV also carried three times more internal fuel than the Mirage III. The aircraft's aerodynamic features were very similar to the III's but required an entirely new structure and layout. This prototype was 67 feet long, had a 37 ft wingspan, 670 square feet of wing area, and weighed approximately 55,000 lb. It was considerably more advanced than the Dassault Mirage III, incorporating new features such as machined and chem-milled planks, tapered sheets, a small amount of titanium, and integral fuel tanks in many locations including the leading portion of the tailfin.

The 01 was an experimental prototype built to explore and solve the problems stemming from prolonged supersonic flight. The sizable technological and operational uncertainties (no plane had yet been found able to cruise at over Mach 1.8 for long periods of time) were only one part of the problem. The weapon-related issues were the other. It took 18 months to build the 01 in Dassault's Saint-Cloud plant near Paris. In late 1958, the aircraft was transferred to the Melun-Villaroche flight testing area for finishing touches and ground tests.

French General Roland Glavany, on a five-year leave from the French Air Force since 1954, took the 01 into the air for its maiden flight on 17 June 1959. For its third flight, on 20 June 1959, the 01 was authorized to fly over the Paris Air Show at Le Bourget airport in front of France's President Charles de Gaulle. On 19 September 1960, René Bigand (replacing Glavany as test pilot) increased the world record for speed on a 1000-kilometre closed circuit to 1,822 km/h (1,132 mph) around Paris and the Melun air force base. Flight 138, on 23 September, corroborated the initial performance and pushed the record on a 500 km closed circuit to an average of 1,972 km/h (1,225 mph), flying between Mach 2.08 and Mach 2.14. The Mirage IV 01 prototype underwent minor modifications during testing in the autumn of 1959, most noticeably, the tail was enlarged (slight reduction in height, large increase in chord).

Further development
In order to increase range, studies were made of a significantly larger Mirage IVB design, powered by two SNECMA license-built Pratt & Whitney J75 engines and having a wing area of 120 m² (1,290 sq ft) compared to 70 m² (750 sq ft) of the prototype IV. This aircraft was to have a speed of Mach 2.4 and weigh 140,000 lb gross, but was cancelled in July 1959 due to cost.

With the Mirage IVB considered to be too expensive, the medium-sized Mirage IVA, slightly larger than the first prototype, was chosen for three more prototypes to be produced. This aircraft had a wing area of 839 square feet and weighed about 70,000 lb These three aircraft were built between 1961 and 1963, with first flights on October 12, 1961; June 1, 1962; and January 23, 1963. The second prototype conducted simulated nuclear bombing runs in the trials range at Colomb-Bechar in southern Algeria. The third prototype tested the navigation system and flight refuelling probe. The fourth prototype Mirage IVA-04 was essentially representative of the production aircraft.

For production, some parts of the aircraft were subcontracted to Sud Aviation (wings and rear fuselage) and Breguet Aviation(tailfin), still a separate company from Dassault until 1967; Dassault manufactured the front fuselage and flight-control system. The first production Mirage IVA was flown in December 7, 1963. A series of 62 aircraft were built, and they entered service between 1964 and 1968. Although Dassault had designed the Mirage IV for the low-level flight role right from the start, the final 12 ordered in 1964 differed from the earlier aircraft in details of the flight controls, avionics, and structural details to improve low-level performance. These changes were later retroactively applied to the whole fleet.

The Mirage IV force soon consisted of nine squadrons of four aircraft (2 pairs—one aircraft carrying the nuclear bomb, one a buddy-refuelling tanker) each, three squadrons each at the airbases at Mont de Marsan, Istres, and St. Dizier. By 1963, most Mirage IV missions were planned as low-level flights.

In December 1963, Dassault proposed a Mirage IV-106 variant with 2 SNECMA TF106 (license-built Pratt and Whitney) engines, an enlarged 105,000 gross-weight fuselage, terrain-avoidance radar, and armed with a proposed French version of the American Douglas GAM-87 Skybolt air-launched ballistic missile. This version would have been very costly, and ultimately was not ordered.

Proposed export variants
In 1963, the Australian government sought a replacement for the Royal Australian Air Force fleet of English Electric Canberra bombers, largely in response to the Indonesian Air Force's purchase of missile-armed Tupolev Tu-16 bombers. Dassault proposed a version of the Mirage IVA with Rolls-Royce Avon engines. Australian Air Marshall Frederick Scherger seriously considered purchase of the IVA in 1961 because it was considered proven hardware already in service (in contrast to the BAC TSR-2 still in development), before settling on the General Dynamics F-111C. The IVA was one of five aircraft types short listed but the General Dynamics F-111C was eventually selected.

In April 1965, the British Government cancelled the BAC TSR-2 reconnaissance-strike aircraft. In response, Dassault and British Aircraft Corporation proposed a modified Mirage IV variant as a replacement in July 1965. The aircraft, known as the Mirage IV* or Mirage IVS (S for Spey) would be re-engined with more powerful Rolls-Royce Spey turbofan engines with a total of 41,700 lbs of thrust, larger (fuselage depth increased by 3 inches, had an approximately 2 foot forward fuselage extension, and was to weigh 80,000 lb), and use avionics planned for the TSR-2, although BAC preferred the French Antilope radar. Although designed by Dassault, the production was to carried out jointly between Dassault and its subcontractors (wing, mid-fuselage, and tail) and BAC (front and rear fuselage). The final assembly location was not determined before this proposal was rejected. The Mirage IV* was to carry a bombload of up to 20,000 lb. While the IV* was claimed to meet most of the RAFs requirements, and to be £1 million cheaper than the American-made F-111, the F-111K was preferred (only to be cancelled in turn) and the Spey-engined Mirage abandoned.

The Mirage IV* met nearly every RAF requirement except for field length, and some claim it exceeded the F-111 slightly in speed and had at least equal range. The estimated cost was 2.321 million pounds per aircraft (for 50) or 2.067 million (for 110), less than the price of the F-111K. British Aircraft Corporation claimed that the British government evaluation into the Mirage IV* was "relatively superficial". However, some British government officials, including Parliament members Julian Risdale and Roy Jenkins, questioned the Mirage IV*'s capacity to operate from unprepared airstrips or to operate at low level, or claimed that the F-111 was a superior aircraft "in a class of its own". However, Bill Gunston notes that low-level Mirage IV missions had been planned since 1963 and Mirage IVs operated regularly at low level since 1965, and argues that the ability of a strategic bomber to operate from unprepared airstrips is historically unimportant. Royal Air Force pilots who test-flew the Mirage IV were "favourably impressed" with its low level performance.

BAC and Dassault had also hoped to sell the Mirage IV* to France and to export the Mirage IV* to various nations, such as India, possibly Israel, and others; the lack of a British sale put an end to such possibilities. Some aviation journalists claim that the rejection of the Mirage IV* may have dampened French interest in joint Anglo-French cooperation.

Design
The Mirage IV shares design features and a visual resemblance to the Mirage III fighter, featuring a tailless delta wing and a single square-topped vertical fin. However, the wing is significantly thinner to allow better high-speed performance and has a thickness/chord ratio of only 3.8% at the root and 3.2% at the tip; this wing was the thinnest built in Europe at that time and one of the thinnest in the world. While being significantly smaller than an expensive medium bomber proposal for the role, the Mirage IV was roughly three times the weight of the preceding Mirage III.

The Mirage IV has two SNECMA Atar turbojets in the rear fuselage, with air intakes on both sides of the fuselage that had intake half-cone shock diffusers, known as souris ("mice"), which were moved forward as speed increased to trim the inlet for the shock wave angle. It can reach high supersonic speeds: the aircraft is redlined at Mach 2.2 at altitude because of airframe temperature restrictions, although it is capable of higher speeds. The aircraft has 14,000 liters (3,700 gal (US)) of internal fuel, and its engines are quite thirsty, especially in afterburner. While the first Mirage IV prototype was fitted with double-eyelid engine nozzles, a more complicated variable geometry nozzle was adopted for production aircraft.

The two-man crew, pilot and navigator, were seated in tandem cockpits, each housed under separate clamshell canopies. A bombing/navigation radar is housed within a radome in the fuselage under the intakes, aft of the cockpit; much of the Mirage IV's onboard avionics systems, such as communications, navigational instrumentation, and bombing equipment, were produced by Thomson-CSF. A refueling probe is built into the nose; aerial refuelling was necessary in most Mirage IV operations as the aircraft only had the fuel capacity, even with external drop tanks, to reach the Soviet Union's borders, thus refuelling was required to allow for a 'round trip'. In the event of nuclear war between the major powers, it was thought that there would be little point in having the fuel to return as the host air bases would have been destroyed; instead, surviving Mirage IVs would have diverted to land at bases in nearby neutral countries following the delivery of their ordnance.

The Mirage IV has two pylons under each wing, with the inboard pylons being normally used for large drop tanks of 2,500 liter (660 gal (US)) capacity. The outer pylons carry ECM and chaff/flare dispenser pods to supplement the internal jamming and countermeasures systems. On current aircraft, these are typically a Barax NG jammer pod under the port wing and a Boz expendables dispenser under the starboard wing. No cannon armament was fitted. The early Mirage IVA had a fuselage recess under the engines for a single AN-11 or AN-22 nuclear weapon of 60 kt yield. The Mirage IV can carry 12 solid-fuel rockets diagonally down below the wing flaps, for rocket-assisted take off (RATO).

From 1972 onward, 12 aircraft were also equipped to carry the CT52 reconnaissance pod in the bomb recess. The CT52 was available in either BA (Basse Altitude, low-level) or HA (Haute Altitude, high-altitude) versions with three or four long-range cameras; a third configuration used an infrared line scanner. The CT52 had no digital systems, relying on older wet-film cameras. During the 1980s, a total of 18 Mirage IVs were retrofitted with a centreline pylon and associated equipment to carry and launch the nuclear ASMP stand-off missile. The Mirage IVA could theoretically carry up to six large conventional bombs at the cost of drop tanks and ECM pods, such armament was rarely fitted in practice.

Introduction and early operations
In February 1964 deliveries of the Mirage IV to the French Air Force started, with the first French Mirage IV strategic bombing squadron being declared operational on 1 October that year. The Mirage IV bomber force, when fully built up, consisted of three wings. These wings were each divided into three bomber squadrons, each with four Mirage IVs, each deployed at a different base to minimise the potential for an enemy strike to knock out the entire bomber force. These squadrons were:


 * 1/91 'Gascogne' based at Mont de Marsan
 * 2/91 'Bretagne' based at Cazaux
 * 1/93 'Guyenne' based at Istres
 * 2/93 'Cevennes' based at Orange
 * 1/94 'Bourbonnais' based at Avord
 * 2/94 'Marne' based at St-Dizier
 * 3/94 'Arbois' based at Luxeuil
 * 3/91 'Beauvaisis' based at Creil
 * 3/93 'Sambre' based at Cambrai

After establishment of its own deterrent force, the Force de Dissuassion, more commonly known as the Force de frappe, France withdrew from the military command structure of NATO in 1966. French President Charles de Gaulle viewed the operational establishment of the Mirage IV fleet, a critical component of the independent Force de frappe, as highly influential to his decision to withdraw France from NATO, and that an independent French nuclear deterrent was necessary to ensure independence as a nation. From 1964 to 1971, the Mirage IV was France's sole means of delivering nuclear ordnance, at this point they were armed with a single 60 kiloton nuclear bomb each.

The primary objectives of the Mirage IVA force were major Soviet cities and bases. With aerial refueling, the plane was able to attack Moscow, Murmansk or Ukrainian cities from French bases. In order to refuel the Mirage IVA fleet, France purchased 14 (12 plus 2 spares) U.S. Boeing C-135F tankers. Mirage IVAs also often operated in pairs, with one aircraft carrying a weapon and the other carrying fuel tanks and a buddy refueling pack allowing it to refuel its mate en route to the target. Even so, some sources state that some of the mission profiles envisioned were actually one-way, with the crew having no chance of returning after bombing a Soviet city.

Initially, the basic attack flight profile was "high-high-high" at a speed of Mach 1.85, engaging targets up to a maximum radius of 3,500 km (2,175 mi). In the late 1960s, when the threat of surface-to-air missile defences made high-altitude flight too hazardous, the Mirage IVA was modified for low-altitude penetration. Flying low, the maximum attack speed was reduced to 1,100 km/h (680 mph) and the combat radius was also decreased. By the 1970s it was clear that vulnerability of the Mirage IV to air defences, even in low-level flight, made the delivery of gravity bombs such as the AN-11 or AN-22 impractical. As more of the deterrent role was passed to land-based IRBMs and submarine-based missiles, one wing of Mirage IVs was stood down in 1976.

Upgrades and decline
In 1973, it was reported that a force of 40 Mirage IVs would continue to perform as a part of France's national nuclear deterrent until the 1980s, and that steady improvements were to be undertaken. In 1979, in response to the decreasing effectiveness of the free-fall bombs used by both its strategic and tactical nuclear forces, the French commenced development of the ASMP stand-off missile, with a range of up to 400 km (250 mi) and a single 150 or 300 kt nuclear warhead. Eighteen Mirage IVAs were modified to carry the new weapon instead of bombs and received the new designation Mirage IVP (Penetration). The first Mirage IVP flew on 12 October 1982 and entered service on 1 May 1986. This variant could carry either a single missile or a reconnaissance pod on the centreline.

In August 1985, a French proposal that would have seen Mirage IVPs stationed at air bases inside neighbouring West German was made public; this deployment would have marked a significant philosophical departure from traditional French nuclear defence policy. On 31 July 1996, the Mirage IVP was formally retired in its bomber capacity, the nuclear mission having been transferred from the Mirage IV to the newer Dassault Mirage 2000N. EB 2/91 was disbanded and EB 1/91 was redesignated Escadron de Reconnaissance Stratégique (Strategic Reconnaissance Squadron), using the 12 remaining Mirage IVPs. In the reconnaissance role, the Mirage IVP has seen service over Bosnia, Iraq, Kosovo, and Afghanistan.

ES 1/91 Gascogne's surviving Mirage IVPs were retired in 2005 and are conserved and stored at the Centre d'Instruction Forces Aériennes Stratégiques (CIFAS) at Bordeaux Mérignac. The retirement of all reconnaissance-configured Mirage IVPs in 2005 meant that the Armée de l'Air's Mirage F1CRs were for some time the only aircraft capable of carrying out aerial reconnaissance missions. The long term replacement for the Mirage IVP was Mirage 2000N aircraft outfitted with a modern PRNG Pod de Reconnaissance Nouvelle Génération (New Generation Reconnaissance Pod), equipped with digital camera equipment.

The Mirage IV had been popular with its crews, who found it enjoyable to fly despite its antiquated systems and generally uncomfortable cockpit. In addition, it required surprisingly little maintenance considering its age and complexity. Royal Air Force pilots who flew the Mirage IV at the Mont de Marsan airbase during its evaluation for the proposed Mirage IV* variant were "favourably impressed" with its low level performance.

Operators

 * French Air Force
 * French Air Force

Aircraft on display

 * 16 is on display at St Dizier airfield.
 * 43 is on display at Mont-de-Marsan airbase.
 * 62 is on display at the Musée de l'Air et de l'Espace at Paris-Le Bourget.