TSR2

by Damien Burke

  Reversionary bombing capability

  With a complex nav/attack system there was always going to be a chance that one or two items within the system could fail during the sortie. Part of the requirement for the aircraft was that no single failure could prevent it attacking its target, so a great deal of effort went into ensuring that the overall system could cope with failures and still permit the crew to carry out an attack, even if it had to be manually flown. For instance, the CCS was responsible for commanding the AFCS to pull up into the loft attack. If the AFCS had failed or degraded and was not responding to CCS commands, the manoeuvre would not be flown. However, a ‘pull up’ light would be energized at the same time, so the pilot could manually pull up, using the g-meter in the cockpit and azimuth lines on the HUD to monitor the manoeuvre. Loss of the SLR for navigation fixes would entail use of the FLR or visual fixes; accuracy would be degraded but should remain within limits for a successful attack. Similar replacements for just about every element of the nav/attack system were available; all would result in loss of accuracy and a higher workload for the crew.

  Attack profiles

  Loft attack

  A typical attack profile for a TSR2 carrying an atomic bomb would be to approach the target at low level at between Mach 0.75 and 0.9 in the terrain-following mode at 200ft (60m), and take a navigational fix when within 30 miles (50km) of the target. This last fix, normally taken using the SLR but possibly taken visually, would enable the attack to be accurate enough to destroy the target with the selected weapon. The Verdan computer was programmed with bombing calculations that would use target position, aircraft fix position, approach speed and preset approach speed to decide when the aircraft should begin the pull-up into the loft manoeuvre. Verdan was programmed with two loft-attack modes, low and high. For each type of loft a constant pitch-up of 5 degrees per second would be flown until a preset angle was reached, with the bomb doors opening shortly beforehand. With the preset angle (30 degrees for low loft, 65 degrees for high loft) reached, the bomb would be released and the bomb doors cycled closed immediately afterwards, while the aircraft continued to pitch at a constant rate for a total of 190 degrees, leaving it inverted and pointing 10 degrees below the horizon. The aircraft would then roll wings-level and continue the dive to escape the explosion. Whether low loft or high loft was used depended upon the yield of the bomb. Higher yields used the high-loft attack, as this gave the bomb a longer trajectory and therefore extended the escape time. Most bombs would be air-bursts, designed to explode at 2,000ft (600m), and accuracy would be in the region of 1,200ft (365m) circular error probable (CEP).

  Loft attack with chandelle escape

  A variation on this attack, the loft attack with chandelle breakaway, modified the procedure. The pitching manoeuvre was terminated at weapons release and the aircraft rolled to 140 degrees bank angle, the pilot holding the bank until the aircraft was headed radially away from the target and then diving to escape.

  Button-hook attack

  For targets of opportunity, or where no fix was possible within 30 miles (50km) and thus accuracy would be unacceptably degraded, the ‘button-hook attack’ was a further option. This involved taking a direct fix on the target itself, either by flying past it and using the SLR to paint the target, or by flying directly over it and taking a visual fix. Continuing to fly away from the target for several miles, the aircraft would then begin a 2g turn to bring it back on course towards the target and begin a low- or high-loft attack. With the last fix being precisely on the target, this was the most accurate type of attack, with a CEP of less than 600ft (185m) expected to be met.

  Over-the-shoulder attack

  A further low-level attack mode was the over-the-shoulder attack. The aircraft would fly directly over the target for a visual fix and then pulled into a climb, pitching at a constant rate until the computed bomb throw matched the distance travelled from the target. This was programmed to be at the 110-degree pitch point, thus throwing the bomb back towards the target. Escape would be made by rolling wings-level and diving, as in the loft attacks. Again a 600ft CEP was the aim, and this was expected to be just about met by this type of attack.

  Laydown

  The aircraft would approach the target at 500ft (150m) and between Mach 0.75 and 0.9, and the target would be fixed when within 30 miles (48km) and overflown, the bomb being released just beforehand. By necessity, all such attacks would be ground-bursts.

  Red Beard, or the nominally 2,000lb ‘Target Marker Bomb’, was not designed for supersonic carriage, and a redesigned casing was initially proposed for external carriage by TSR2, though not proceeded with. Damien Burke

  Medium-level attack profiles

  Level attack

  The first medium-level attack was a simple Second World War-style bomb run. Approach at 25,000ft (7,600m) and Mach 1.7, take a fix within 30 miles (50km), fly straight over the target, releasing the bomb when its throw is computed to match the distance to the target, and continue straight and level to escape. Although 1,200ft (365m) CEP was the requirement here, BAC believed it an unlikely possibility, given the limitations in SLR fix accuracy and the distance the bomb had to fall.

  Dive toss attack

  Far more likely to hit the target was the medium dive toss attack. In this case, the approach was the same as for the level attack, but at a computed distance from the target the aircraft would bunt at 1/2g into a 17.5-degree dive to point at the target. Visual means would be used to take another fix on the target during the dive. At a predetermined slant range from the target (25,000ft (7,600m)) the aircraft would pull out of the dive and effectively begin the later stages of a loft attack, pitching up at a constant rate until the computed bomb throw matched up with the target and the bomb was released. Escape would be identical to the loft attack, with or without chandelle. The blind dive toss attack was later deleted, though visual dive toss was retained.

  Nuclear strike

  The UK’s first tactical nuclear bomb was developed to OR.1127, the weapon itself being named Red Beard and often referred to as a ‘Target Marker Bomb’ in an amusing attempt to hide its true nature while allowing discussion of its dimensions and approximate weight. The carriage of just one of these weapons, to be held within the aircraft’s bomb bay, was initially required by OR.343. Of nominal 2,000lb (900kg) weight (the bomb actually weighed around 1,700lb (770kg)), both versions of Red Beard were just over 12ft (3.6m) long and had a diameter of 28in (71cm). The Mk 1 version had an explosive yield of 10 kilotons, and the Mk 2 a yield of 25 kilotons. The RAE’s Working Party on Weapons for the Aircraft to OR.343 had found that most ‘hard’ targets (reinforced structures) would require a yield of 32 kilotons, and that only softer targets could therefore be destroyed by Red Beard. The weapon’s fuzing system also introduced limitations to its use. Red Beard was designed to be released in a loft attack, with the aircraft pulling into a climb before release. The bomb would be ejected and also continue to climb, with the fuzing mechanism activating once a pre-set altitude was reached. Thus a laydown attack, releasing the weapon from low-level flight without climbing, or a shallower loft attack was not possible. (In the former the weapon would never be fuzed, and in the latter the releasing aircraft would not be able to escape before the weapon exploded.) These limitations, plus the single yield setting for each mark of the weapon, led, in November 1959, to the Air Staff deciding against the carriage of this weapon on the OR.343 aircraft, and they decided to begin work on a new requirement for a more modern and flexible bomb; this would be ASR.1177. For the time being, however, development had to continue as if Red Beard would still be used, there being no readily available alternative.

  In mid-1960 the Air Staff raised the stakes on OR.343 with a request to upgrade the requirement, changing to the carriage of a pair of nuclear bombs. (While the TSR2 was then scheduled to replace Canberras on a one-for-two basis, the number of targets with which the force was committed to deal was not going to reduce.) Red Beard, a big and heavy bomb, c
ould only have been carried in pairs externally, and would have seriously reduced the aircraft’s range as a result of the increased weight and drag. The tail unit was also suspected to be only viable if the bomb was released at speeds below 750kt (860mph; 1,390km/h), though the bomb was capable of surviving the expected levels of temperature and vibration to which it would be subjected when carried externally. All of this certainly supported the Air Staff’s decision in November 1959 to move on from Red Beard to something better. The American Mk 28 weapon was looked at instead, as it had already been considered for use with the Canberra interdictor force and was small enough to be carried as a pair internally. In October 1960 OR.343 was modified to include provision for the carriage of either one weapon (internally), a pair of the right size internally or a pair externally, the paired weapons being Mk 28s or a possible British future weapon (ASR.1177), and Red Beard if there was no other option.

  Air Staff Requirement 1177 called for an improved tactical nuclear bomb for low-level deployment. This would eventually result in the WE177 bomb, of significantly smaller size and weight than Red Beard. By January 1961 it was also clear that all existing stocks of Red Beard would be past their ‘use by’ dates, and the weapon out of service by the time the first TSR2 strike squadron was formed, but once again there was no alternative but to continue to develop the aircraft to carry Red Beard as well as the American Mk 28. After the first WE177 warhead was successfully detonated at a test site in Nevada in March 1962, TSR2 weapons planning began to firm up, and references to Red Beard/1127 weapons progressively disappeared and were replaced by references to ASR.1177, and later specifically WE177A. This was to be a bomb of similar destructive power to Red Beard Mk 1, with a yield of 10 kilotons. Owing to its significantly reduced size compared with Red Beard, it was hoped it could be carried as an internal pair (in tandem), and the ‘insurance’ requirement of carrying Red Beard was reverted to the original idea of carrying a single weapon internally, then dropped entirely in December 1962 (though it continued to appear in some RAF correspondence, prompting a final formal cancellation of the requirement to carry it as late as September 1963).

  As well as the American Mk 28, the American Mk 43 was considered for TSR2s assigned to NATO. The bomb bay was neither wide enough nor long enough to accommodate a pair of Mk 43 No. 2s, the preferred weapon because of its higher yield. The Mk 43 was also subject to environmental limitations in terms of temperature, release speed and vibration, all of which would preclude external carriage. The Mk 43 No. 1 was a lower-yield weapon, 14.5in (37cm) shorter and thus able to be carried in pairs internally. Similarly, Mk 57s could be carried as pairs within the bomb bay. As costs rose and economy measures were sought, this variety of possible armament came under fire and gradually the options were narrowed down. An approach was made to the Americans via the US National Military Representative at SHAPE on 20 November 1962, to ask about availability of Mk 43 bombs for the TSR2 force. The response did not arrive until December, and it was not positive. As the question had been asked just weeks after Skybolt’s cancellation, it was no surprise that it had become mixed up in the less-than-friendly negotiations between the Prime Minister and the US President about the future of the UK’s nuclear deterrent. In late 1960, after examination of the strategic possibilities of TSR2, this ‘bonus’ capability had been considered to be a possible insurance against the failure of Skybolt. The aircraft was now in precisely the position feared in 1960.

  A Red Beard windtunnel model drop in simulated release conditions of level flight at 25,000ft (7,600m) and Mach 0.88. BAE Systems via Brooklands Museum

  A mockup of the American Mk 43 nuclear bomb mounted on the mockup TSR2. These weapons were too large to allow more than one to be carried internally, so if two were carried they would have had to be mounted externally. BAE Systems via Warton Heritage Group

  A Mk 43 mockup, single internal carriage. It was for this sort of configuration that the TSR2 was originally required, albeit carrying Red Beard rather than an American weapon. Note the baffle plates with circular holes that surround the forward section of the bomb to reduce turbulence within the bay with the doors open. BAE Systems via Warton Heritage Group

  Internal carriage of twin WE177s, tandem configuration. The more powerful variants of WE177 were too long to be carried in this manner. BAE Systems via Warton Heritage Group

  Internal carriage of twin WE177s, side-by-side configuration. With the bay and doors originally designed to accommodate Red Beard, the doors had to be dished to accommodate other stores, and side-by-side carriage of WE177 required further indentationss to make room for the fins, as seen on the extreme edges of this photo. BAE Systems via Warton Heritage Group

  By July 1963 plans centred almost entirely around the use of WE177, the scheme being for the world-wide TSR2 force to be assigned a stockpile of seventy-six of these weapons, plus a further eight to be held in reserve. The low yield (10 kilotons) of WE177A, the first version planned, was a product of the Prime Minister’s edict in July 1962 that tactical nuclear weapons should be low-yield in order to try to stop limited tactical nuclear use escalating into a full-scale nuclear war. Many of the RAF’s assigned targets in the event of nuclear conflict could not be effectively destroyed by a single such weapon, and this prompted some discussion on the use of multiple weapons on a single target; in effect, stick bombing using nuclear weapons. This meant that the requirement to carry just a pair of WE177s now had to be rethought, and the obvious solution was to double this and carry a pair internally plus one under each wing. The incorporation of a suitable timed-release device into the nuclear bomb release panel to enable stick bombing was another addition to costs, but in the end this facility was not required, as by August 1963 it had become clear that fifty-three of the weapons assigned to the TSR2 force would in fact be higher-yield (300-kiloton) WE177Bs. Accordingly the requirement to carry up to four weapons simultaneously was dropped, to BAC’s relief. A pair of WE177Bs could be carried internally, side-by-side.

  Another view of the side-by-side WE177 configuration. The forward end of the bay was left clear for a weapons bay fuel tank. BAE Systems via Warton Heritage Group

  The carriage of US nuclear weapons had been attractive when WE177 was still in doubt, but now that it was nearly a sure thing, the disadvantages of carrying US weapons became overwhelming. The USA had strict controls and procedures to deal with when it came to carrying (and indeed using) its weapons. Dispersal of the TSR2 force would be very difficult, as it would need prior arrangement and the co-operation of the US guard forces. In exercises, Vickers Valiants equipped with US weapons had been so held up by this issue that it had been calculated that they would have been destroyed on the ground before a dispersal operation could have been started. On the other hand, TSR2s with British weapons could disperse at a moment’s notice; and strike any target the UK wanted to hit without the need for prior US approval.

  After TSR2’s cancellation, WE177 development changed tack, and WE177B became a larger and much more powerful version, with a yield of 450 kilotons. This was the first to enter service, being carried by RAF Vulcans and later by Tornadoes. The WE177A had a dual role as a low-level tactical weapon and also a nuclear depth charge (with yield limited to 0.5 kilotons for situations where 10 kilotons would endanger non-combatant or friendly shipping), and ended up being mainly used by the RN’s anti-submarine helicopter force. A third version, WE177C, of approximately 200 kilotons yield, was deployed by RAF Germany’s Jaguars and Tornados. Had the TSR2 continued, it would probably have been this version that it would have ended up carrying, though its increased size would have precluded the carriage of more than one internally.

  A WE177C training round. This would probably have been the version of WE177 most often carried by the TSR2 force, had the project not been cancelled. Damien Burke

  A windtunnel model with Matra rocket pods mounted on light stores pylons. BAE Systems via Warton Heritage Group

  Conventional strike

  Conventio
nal strike was regarded by the Air Staff as very much a tertiary role, and they resisted any attempts to develop dedicated weapons for the type, instead preferring to use existing bombs and rockets, despite the obvious shortcomings of relying upon weapons that were not designed to be carried in the temperature and vibration conditions expected to be experienced by the TSR2. They also neglected to specify any kind of conventional weapon sighting for the aircraft other than the visual dive attack.

  Rockets

  The ‘battleship broadside’ effect of a well-executed rocket attack was particularly effective against soft and medium targets, such as troops, vehicles, aircraft on the ground and lightly constructed buildings. However, an aircraft firing rockets is burdened by a number of limitations in speed, approach angle and visibility, so rocket attacks would only have been possible on relatively lightly defended targets, which OR.343 recognized.

  Early studies by the Air Staff into rocket effectiveness resulted in them requesting that OR.343 would include a requirement for 2in rockets in pods of thirty-seven rockets each, which could be mounted both on underwing pylons and also within the bomb bay, from where they would be lowered before firing, and also for 3in rockets mounted on standard underwing rails (as used by Hunter fighter/ground-attack variants). The RAE and the MoA objected to the plan to carry standard pods within the bomb bay and the associated cost and complexity of a lowering mechanism, and suggested that a dedicated rocket pack housed in the bomb bay would be a cheaper solution (quite how they came to this conclusion is unclear). It did not take long for the rocket situation to be simplified. By November 1959 the requirement to carry 3in rockets was under consideration for removal (and was indeed deleted by October 1960), and for 2in rockets the use of standard under-wing rocket pods was being considered (these soon became preferred to the development of any special-to-type weapons-bay rocket pack). With the acceptance that standard existing pods would be used, no particular extra development was needed, and it was not until August 1964 that wind tunnel tests began, using scale models of the underwing pylons and standard Matra rocket pods. These showed that the pylons needed to be stiffer, and that the pods themselves would benefit from the fitting of small fins, but no further work was carried out before the project was cancelled.