The Marshall contribution
Marshall of Cambridge (Engineering) Ltd, now called Marshall Aerospace, became involved in the first of three significant modification schemes for the Hercules, specifically related to the needs of "Operation Corporate", in the late afternoon of 15th April, and design activities began at Cambridge Airport, which the company owns, that same night. Thus began a period of intensive design, development, conversion and flight testing that would eventually involve 20 of the RAF's fleet of Hercules C Mk 1’s; although not all of these were completed by the time the conflict ended in the Falklands, all have now been redelivered to the RAF.

The company was no stranger to the Hercules, and was the obvious choice for these rush conversion schemes to install flight refuelling probes (Mod 5308) and Omega navaids (Mod 5309), and to convert aircraft as air refuelling tankers (Mod 5310). As already noted, Marshall of Cambridge had been designated as the technical centre to support the RAF Hercules in 1966, and had also become a Lockheed-authorised Service Centre for civil and military C-130s in 1975. It has also undertaken the repainting of the entire fleet, from its original sand-and-stone, with black undersides, to the NATO standard green-and-grey with light grey undersides; has converted the single W Mk 2 for the Met Research Flight; has replaced the wing centre sections to extend the aircraft's service life, and is now engaged in re-skinning outer wing torsion boxes for the same objective.

The wing modifications on the Hercules were aimed at extending the service life to meet RAF requirements well into the next century. To validate the refurbishing of the outer wing, a complete tip-to-tip specimen (less leading and trailing edges) was used at the start of an extended fatigue test at Cambridge, in a rig with 24 servo-controlled hydraulic jacks applying loads under computer management and control. Based on an analysis of the RAF Hercules fleet's fatigue meter readings for which Marshall is in any case responsible - a representative profile has been built up for the test specimen, combining nine varying, typical, mission loadings, and the rig will apply these loadings cyclically to represent 1,000 flying hours (about 400 missions) in every 100 hrs of real time; thus, the fatigue test to continue over about two years in order to represent 60,000 flight hrs (for a 20,000 hr life with a three-to- one factor), will soon surpass the hours actually flown by any of the fully modified aircraft expected in service.

The company is also now well advanced with the programme to convert Hercules C Mk 1s to C Mk 3s for the RAF. The first Marshall conversion was flown at Cambridge on 10th January 1980 and the 20th aircraft (excluding the original conversion by Lockheed) was late 1982. While the downtime to complete a conversion has decreased along the learning curve, however, the rate at which the RAF can afford to have the work completed has slowed, and it was 1985 before the last two were redelivered; whereas two aircraft at a time were handled at Cambridge originally, only one is now being "stretched" at any one moment. kits, including the two extra fuselage barrel sections of 100 in (254 cm) and 80 in (203 cm) that are inserted, respectively, ahead of and behind the wing, are purchased from Lockheed-Georgia.

Stretching a Hercules involves stripping the fuselage of all interior sound proofing and disconnecting the numerous control and system runs, before removing bolts at the front and rear fuselage joints. As well as inserting the new sections at these two joint positions, two upper longerons in the fuselage are replaced, using heavier gauge components, and the lower fuselage adjacent to the new section has to be modified to maintain a constant section. Additional lengths of electrical wiring, control cables, hydraulic and oxygen pipes, and air ducts have to be inserted before the new floors are fitted, soundproofing restored and new external and internal finishes are applied.

Despite this very considerable experience with the Hercules, and the fact that Marshall of Cambridge has been involved in some way with the design or development of virtually every type of British aircraft since the end of the War, the company had had no previous direct experience of air-to-air refuelling when it received the instruction to proceed with installation of a flight refuelling probe. The probes themselves were standard RAF issue - there was no time to have new probes manufactured and they were therefore "donated" by those Vulcans not themselves needed for "Operation Corporate" Using a Hercules (XV200) already positioned at Cambridge for its major service inspection, Marshall completed the first installation within 10 days, and after ground testing, made the first flight with probe fitted on 28th April. This first probed Hercules was then delivered to the A&AEE, Boscombe Down, next day and made its first "wet" coupling with a Victor tanker on 2nd May, followed by two more couplings (one at night) on 4th May 1982 and delivery to RAF Lyneham on 5th May 1982.

The probe, with a Mk 8 nozzle, is mounted on the upper forward fuselage, offset to starboard; from it, the in-flight refuelling pipe (of 3in / 7.6cm diameter) is routed aft along the upper surface of the fuselage, to enter the wing trailing edge-to-fuselage fairing on the starboard side, and thence connect with the vertical ground refuelling pipe.

The latter has been modified to have a "Y"-branch, adjacent to which is a non-return valve to isolate the in-flight refuelling system when the aircraft is refuelled on the ground; another such valve just aft of the probe serves to contain fuel in the event of nozzle failure at the weak link, which can result from excessive side loads applied in the rare case of a badly-aligned contact between probe and drogue.

Two floodlights were fitted to the side of the co-pilot's instrument panel and positioned to illuminate the probe from the right-hand windows, and the refuelling control panel was located above the navigator's station on the flight deck. The aircraft fitted with probes came to Marshall in the LR2 configuration (with two long-range tanks in the fuselage) and with the probe fitted became known, for convenience, as Hercules PLR2s. Only C Mk 1’s were converted during Operation Corporate - 16 in all.

Before the first PLR2 had reached Lyneham, Marshall had been asked (on 30 April) to introduce Omega equipment on the Hercules, to provide an additional navaid for the long range flights over the South Atlantic. The second probed aircraft (XV179) served as the guinea pig for this installation, with an aerial located in the upper rear fuselage (to port of the fin), and the display and controls at the navigator's station. The complete programme, from initiation to delivery of the first Omega-equipped aircraft to Lyneham, took 14 days (first flight being made on 12 May for CA release), and all the aircraft eventually fitted with probes also have Omega.