Heavyweight of choice?

The tank transporter, or perhaps more accurately, the heavy equipment transporter (HET) will not be the most numerous ‘truck’ in the inventory of any armed force, it’s number seldom exceeding a third of the to-be-transported heavy armour fleet. However, despite those relatively small numbers, it will most definitely be one of the most important ‘trucks’ in any fleet, and is also very likely to be the most expensive.

Like any ‘truck’ used for almost any role within the military, type/configuration options for a HET are numerous. These can start with what is essentially a commercial tractor unit painted green or tan, with a rack for the drivers’ rifle, and progress right through to a purpose-designed fully tactical option. That same variety of choice applies to the all-important, but so often overlooked, semi-trailer.

User choices for a HET are driven my many factors, not least budget, with a basic ‘green/tan painted’ commercial option coming in at less than half the purchase price of a fully tactical, designed-for-purpose alternative. That fully tactical, designed-for-purpose alternative, albeit a more expensive alternative to acquire will of course have greater longevity, will probably have refurbishment/rebuild factored into its design, and will of course be better suited to deployed and/or combat operations.

Pressure to comply with various aspects of commercial transport legislation can also impact quite heavily on type choices, particularly for a NATO-grade armed force, and even more so for those within the EU. Clearly the more tactical and military-specific any design is, the less likely it is to fully comply with current/pending commercial transport legislation.

Acknowledging that when compared to a ‘fully tactical’ counterpart, a legislatively-compliant design will almost certainly be more user-friendly on a day-to-day peacetime basis. However in a deployed and/or conflict situation, the fully tactical counterpart will be the better-suited of the two options.

Legislative compliance issues can begin with what appear to be the simpler things such as vehicle lighting, or the location and type of recovery/towing points, and include factors such as overall height or even turning radius. Using the latter as an example, even a four-axle tractor unit with ‘normal sized’ commercial tyres can meet these requirements with relative ease, but for a unit of comparable dimensions (including overall width and wheel track) fitted with the much larger 16.00 R 20 single off-road tyres, the issues can be very real.

At the most significant end of the scale, emissions compliance is regularly a topic of heated debate. No matter what claims are made, it remains fact that no engine which is current EU/EPA emissions compliant will run continuously on jet, low-grade/high-sulphur or even ‘dirty’ fuel, for extended periods without limitations of some sort. A far simpler, albeit still EURO 3-compliant unit, is without doubt a far more practical option for such usage.

Similar compliance issues arise with the semi-trailer. Once little more than a wooden-floored flatbed on an I-beam frame with leaf-sprung walking beam suspension, the modern HET semi-trailer is now a highly complex piece of kit, and something that can cost almost as much as the tractor unit it is coupled to. The specification differences between a fully commercially-compliant semi-trailer that can transport an MBT and the ideal tactical option, are even wider than those of the towing tractor. The laws of physics dictate that for all-terrain stability, an ideal HET semi-trailer will have a load bed and track comparable to the width of its primary MBT payload. As an example case the Leopard 2A6 comes in at 3.75 m. Axle numbers should be the minimum required to meet desired ground pressure (usually five, occasionally six), and tyres should be something akin to 24 R 21 wide footprint singles.

If there are HET procurement trends to be identified, then any trend with semi-trailers is far clearer than that for tractor units. To allow for relatively trouble-free peacetime usage, almost without exception NATO/EU users are opting for a legislation-compliant option, albeit one that is as all-terrain capable and high-performing on deployment as technically possible. Trailer (without extending ‘greedy’ boards) width and/or wheel track is usually 3 m, and while some do occasionally bite the bullet and go wider, in order to comply with height limitations, axle loadings and turning requirements, most now opt for up to 8 pendular suspended axle rows (many of which steer), fitted with up to 64 road-biased tyres (up to eight per axle row), that are around two-thirds the diameter of an off-road option such as the 24 R 21.

With tractor units, as previously mentioned, it remains possible to procure a capable tactical option that is for the most part legislatively compliant. Large 1600 R 20 off-road single tyres, military-specific cabs, deep fording, winterisation, full EMC compliance and other military demands, for the most part can be engineered in and within current legislation. However, this is becoming more difficult year-on-year as commercial legislation is requiring ever more driver aids and safety systems to be fitted as standard. Quite frankly, if left to their own devices on deployed operations, these can be a life-threatening tactical liability.

With tractor units, there is less agreement over procurement direction than there appears to be with trailers, and while in most instances within Europe, EU standards compliance is an ever-present procurement bane, users still vary widely in their choices. A typical example given later in this piece is that of neighbours Norway and Sweden.

The perfect scenario for HETs would of course see an armed force having two fleets, a peacetime fleet that complies fully with all legislation, and that can run on roads and possibly even prepared tracks, and a tactical fleet that puts capability ahead of all else, including compliance with legislation. Regrettably, that perfect scenario is simply not affordable in the modern world, and in truth it probably never was, even in the Cold War world which tended to lean towards a capability ahead of compliance policy with most military procurements. As previously outlined, leanings these days do tend to be the other way, with legislative compliance over full tactical capability being the direction taken. A genuine designed-for-purpose HET is now something of a rarity.

The user conundrum

Using Europe/NATO as a sizeable test subject, a glance through inventories will show that no two users currently operate the same HET, and while there is inevitably some commonality in brand of tractor truck if not exact model, there is even greater variety in the semi-trailer department. The HET trailer has traditionally been seen as the local production ‘carrot’ by the tractor unit manufacturer, the usual prime contractor for a HET contract award. However, with the size and weight of payloads ever increasing, the ability to design and manufacture a trailer that complies to any degree with legislation while remaining a viable load carrier on anything on than level metalled roads is becoming ever more difficult to do. Such a capability is now considered beyond that of many legacy suppliers of HET semi-trailers. Additionally, with semi-trailers generally outlasting their original tractor units by means of design simplicity in general, the increasing size and weight of payloads is also becoming an issue for those that wish to retain, refurbish and reuse existing trailers with a new tractor unit.

Based on age, within Europe/NATO a number of armed forces either are currently, or in the near-term will be looking to replace their current HET fleets. A most definite front-runner for those that have yet to decide on a replacement HET has to be the Rheinmetall MAN Military Vehicles (RMMV) HX81 tractor truck, and for those that require a degree of legislative compliance combined with a tactical capability, potentially with a Doll-produced semi-trailer.

Before taking a closer look at the HX81, its recent successes, and potential future opportunities, a quick run through of the opposition is in order. This run will not cover semi-trailers, just tractor trucks, and will be a non-technical, range-specific overview.

Europe’s ‘big seven’ commercial truck manufacturers all offer commercial heavy haulage options that can haul payloads equal to those of even the heaviest MBTs with ease. However, not all of these manufacturers directly offer a true military HET option.

Daimler, Scania and Volvo offer commercial models with varying degrees of militarisation, these options including armoured cabs. Daimler has the added option of two distinct and different models, the cab-over-engine (COE) Arocs, or the bonneted Zetros. Renault could offer a mildly militarised commercial model directly, although for higher levels of militarisation this would likely be offered via or in conjunction with Arquus, which is essentially the former Renault Trucks Defence. IVECO’s defence division IVECO Defence Vehicles (IDV) can offer variants of the new Modular Military Range (MMR) that has options including commercial or military-specific cabs. Technically, should any requirement call for a ‘green panted’ truck, IDV could offer an appropriately-specced IVECO commercial model. For completeness, Renault is owned by Volvo, while Scania and MAN (along with Volkswagen) are part of TRATON Group.

DAF (owned by US company Paccar) does not technically offer an all-wheel drive and/or military product. However, it should be noted that Belgian armed forces are currently receiving a batch of TATRA Phoenix (including a small number of HETs) that are badged and promoted as DAF. TATRA’s Phoenix is a heavy/severe-duty design that uses a DAF cab and Paccar engine (Paccar is DAF’s parent company), and the Belgian deal involves local content by DAF. TATRA also has the option to offer users the military-focused T815-7; this and the Phoenix range are based on TATRA’s unique tubular backbone-type chassis and swinging half-axle suspension arrangement.

Realistically, the above are the most likely competitors for the HX81, and most certainly within Europe. As far as the ‘big seven’ commercial truck manufacturers are concerned, MAN’s TGS heavy commercial range has technically not been overlooked. RMMV is a 51/49% joint venture between Rheinmetall and MAN Truck & Bus AG, and this entity is responsible for global military sales of MAN trucks. So, as part of the TG MIL range, the TGS series could be offered by RMMV should any user require a more commercially-based solution than the HX81.

Not to be overlooked as a potential European competitor for RMMV in limited markets is Sisu, Finland’s specialist producer. Sisu offers the Polar range, these are purpose-designed chassis, but with Daimler (Mercedes-Benz) aggregates and cab. While the range currently does not include a HET, it would not be beyond the capabilities of specialist manufacturer Sisu to design and produce one. Finally, BMC of Turkey offers a HET derivative of its latest Tugra commercial range.

Beyond Europe, there are a variety of heavy truck manufacturers, but not all have any real interest in the military marketplace, and in particular more specialist variants such as HETs, while others such as those based in countries such as Belarus, China, Iran or Russia, are of little or no real relevance to the European military truck market.

For completeness though, Belarus is of course home to MZKT and MAZ. MZKT was the former supplier of multi-axle transporter, erector, launchers (TELs), HETs and similar vehicles to Russia and many Warsaw Pact armed forces. China is awash with heavy truck manufacturers, most capable of producing a HET of sorts. For now the PLA appears to be procuring two broadly similar military-specific HETs from Taian Aerospace Special Vehicle Co., Ltd. (TASV) – the Taian TA4360 and TA4410. Iran appears to be receiving HETs that are based on Volvo designs/models, although details regarding the actual sourcing/production of these are sketchy at best.

Russia, following the effective loss of MZKT with the independence of Belarus turned primarily to BAZ and Kamaz to fill a very large specialist vehicle void. For the last decade, the HET of choice for Russia has been the Kamaz-65225, a HET derivative of the commercial Kamaz-6522. For reasons unknown (which could vary from Russian industry’s inability to develop a viable replacement for the older MAZ-537, through to pure economics), the Kamaz-65225 while all-wheel drive is 6×6, not 8×8, and is fitted with twin rear wheels/tyres, rather than the larger single configuration of the MAZ-537. The standard semi-trailer for the Kamaz, and indeed all HETs mentioned in this paragraph, while not fitted with wide footprint all-terrain tyres, do have significantly larger diameter wheels and tyres than their western counterparts. Perhaps most interestingly, all their load platforms are full-width (the width of their payload), and not reliant on the stability-limiting ‘greedy boards’ that are required for full road usage compliance within the EU.

Returning to worldwide competitive possibilities for the HX81, the most obvious of these would be the US Army’s current HET of choice, the military-specific Oshkosh M1070A1. For compliance with European roads, the M1070A1 has been modified and is designated the M1300, and this operates with a European legislation compliant M1302 semi-trailer supplied by Broshuis. The ongoing US Common Tactical Truck (CTT) program could evolve to offer the US Army options in the HET segment, but it is considered likely that procurement of the M1070A1/M1300 will continue in the near- to mid-term. Since its introduction in A0 configuration, Oshkosh has actively marketed the M1070 worldwide, and while the UK is the only European operator of a derivative of the type, it is known to have performed well.

Also from the US, Mack and Navistar both potentially have options. Mack, owned by Volvo, is again active in the defence arena and a military HET based on the Granite commercial platform should be relatively easy to develop. Navistar Defense also has options. Navistar Defense is now a standalone company, 70% owned by Cerberus Capital Management, the remaining 30% retained by Navistar, Navistar itself part of TRATON. Navistar has previously delivered HETs, the most recent known customer being Israel, for which the company extensively revised a commercial model, adding a selection on non-standard heavier duty/capacity COTS components to the specifications.

Front runner

Returning to the HX81, with seven known current customers or users, the type is pretty close to being market leader within Europe and European-accessible markets. Additionally, as previously noted, it looks likely to be a serious contender for a selection of current/pending HET requirements within those regions.

Current users or customers of the HX81 are Australia, Austria, Germany, Norway, Saudi Arabia, Ukraine, and the UAE. Australia, in July 2013 and as part of the wider Project Land 121 (Overlander) Phase 3B ordered an estimated 110 HX81s, 21 of which are fitted with a Rheinmetall armoured cab, the remainder with the standard HX range military-specific flat-panelled cab. Trailers as local content are supplied by Haulmark Trailers, these are a very specific design configuration to comply with Australia’s stringent axle weight laws.

Austria ordered an initial four HX81s, and as part of a frame contract awarded to RMMV in 2023 for up to 1375 trucks has ordered a further 15, with an armoured cab and an eight-axle Doll semi-trailer.

When deliveries conclude this year, Germany will have received a total of 158 HX81 HETs. The original 21, which included two qualification vehicles, are fitted with a KMW armoured cab, while the remaining 137 examples are fitted with the standard HX range unprotected cab. There are some other limited configuration differences between these and the original 21 delivered.

Norway’s HX81s are, as of early 2024, in production. Norway and Sweden are both procuring RMMV trucks under a joint procurement project fronted by Norway’s Defence Logistics Organisation (NDLO). Highlighting an earlier comment regarding a lack of commonality in HET procurement across armed forces, this fact is further reinforced when it is noted that even under a joint procurement project, Norway may be procuring HX81 for a HET role, but Sweden has opted for a far less tactical TG MIL-based solution.

In 2016 an undisclosed international customer, now known to have been Saudi Arabia, awarded Rheinmetall a contract for 110 HX81s with semi-trailers. Due to export licence issues it is believed that only 20 tractor units and all trailers would be delivered. Following a potential sale to Jordan and then Romania, in 2023 it was revealed that the 90 remaining HX81s, together with full-width three-axle Doll, tactical semi-trailers would be supplied to Ukraine by Germany. The original semi-trailers are understood to have been Nicolas-suppled five-axle full-width examples with 24 R 21 wide footprint tyres, and an APU-driven axle for additional traction off-road

The first export user of the HX81 is understood to have been the United Arab Emirates (UAE). Between 2011-2014 it is understood that 32 (4 + 28) HX81s with 28 Crossmobil five-axle full-width semi-trailers were delivered. Most HX81s have an extended version of the standard RMMV modular military cab, and the rear two drive axles have the standard 16.00 R 20 tyres replaced with wider 24 R 21 tyres, as fitted to the semi-trailer.

Looking ahead, there are three pending requirements within Europe that immediately spring to mind, these in France, the UK and the Netherlands. France has a definite need to replace a near 30-year old fleet of purpose-designed Renault TRM 700-100 HETs, and while in more recent times these have been supplemented by less capable Sisu E-Tech 480, the need for replacement remains. Recent truck winners in France have been Renault/Arquus (perhaps understandably) and Scania, with the latter also having a truck manufacturing plant in France. If France desires a true tactical option, neither Scania nor Renault have anything in their respective portfolios that can match the HX81 in this area.

With regard to the UK, the current Oshkosh 1070F HETs were procured under a private finance initiative (PFI), and a decision on whether or not to extend this is imminent. The UK has definitely reaped the benefit of a tactical HET on global deployments in recent years, and even supplemented the originally procured road-biased semi-trailers with a more robust off-road solution for use on deployed operations. Should the UK opt to replace its current Oshkosh HETs, given the standard British Army truck fleet consists of RMMV HX models, the HX81 would have to be a serious competitor, even against the latest M1070/M1300 which has been selected by the US for operating in Europe.

The HX; oily bits and beyond

RMMV (then MAN), confirmed development of the HX tactical range of trucks in 2003, and the launch customer for the HX range was the UK MoD. The revised HX2 range entered production in 2015, with the final original HX models (HX77 for Australia) delivered in 2023. In technical terms, the HX81 combines elements of both HX and HX2 ranges. With the HX range RMMV has strived for maximum commonality with the TG commercial product, the aim being to reduce procurement and through-life costs. Given the very specific nature of a tactical military HET design, the number of model-specific components or modifications is greater than with a standard HX range truck.

The HX81 is entirely conventional in design and based on a single-piece C-section ladder-frame chassis. Early HX81 designs featured a chassis that was essentially a shortened version of the chassis of the HX77 8×8, with later HX81 designs incorporating the front section of the HX2 range 44M 8×8. HX chassis are derived from the commercial TGS chassis, the primary differences being the cross members, which are HX-specific to enable the higher degree of torsional twist required for an off-road design. The wheelbase of the HX81 is 1.8 m + 3.2 m + 1.5 m, although options are stated to be available. The original two HX81s delivered had a slightly shorter tandem to tandem wheelbase of 2.95 m. Maximum permissible gross combination weight (GCW) is 130,000 kg. Gross vehicle weight (GWV) rating (unladen plus imposed fifth wheel load) can vary by configuration, but maximum permissible is now 45,000 kg, up from its original figure of 44,000 kg.

The HX81 can be fitted with a selection of cabs, options including two swap-cab armouring solutions that are known as the Integrated Armour Cabin (IAC). The IAC was originally developed in conjunction with Krauss-Maffei Wegmann (KMW) for the SX range of trucks. A Rheinmetall-developed IAC option is now available. The first 19 HX81s ordered by the German Bundeswehr are fitted with the KMW IAC. Australia and Norway have both opted for the Rheinmetall option for their HX81s fitted with an IAC. The unarmoured cab fitted to the HX81 is the latest version of RMMV’s modular military-specific cab, this tracing back to the Category 1 trucks that entered service in 1976. The HX range evolution of the modular military-specific cab is 290 mm deeper than its immediate predecessor, and has more than 600 litres of gross stowage space in the rear. This is sufficient for radio equipment and the full kit of three soldiers. In its extended configuration, this cab can seat up to six if required. The bulk of the instrumentation package has been taken from MAN’s TG WorldWide commercial range, as this is deemed more practical and cost-effective than the purpose-designed instrumentation of earlier cabs.

The detachable hard-top roof accommodates the optional air-conditioning equipment, plus a nuclear, biological, chemical (NBC) filtration system for the over-pressured cab if required. The roof is reinforced to take the weight of two soldiers and withstand the recoil forces of a 12.7 mm heavy machine gun in a ring-mount. A blast-proof vertical split-windscreen is fitted as standard, and a riot protection kit is available for the cab. Appliqué protection kits, for which vehicles are prepared to accept at the production stage, have also been developed for this cab, in conjunction with Ressenig of Austria and Rheinmetall of Germany. Known as the Modular Armour Cabin (MAC), in basic specification the weight of these kits is about 1,500 kg, and it would be technically possible to fit the ballistic protection elements from these to the HX81 should it be required.

The 132 HX81s ordered by the Bundeswehr in 2018 are being fitted with the unarmoured cab. In configuration the cab will be very similar to the cab fitted to the Ungeschützte Transport Fahrzeuge (UTF; ENG: Unprotected Transport Vehicle) HX42M (6×6) and HX44M (8×8) family of vehicles, the contract for which was awarded to RMMV in July 2018. The unprotected cab of the HX81 can be exchanged for the protected IAC version if required.

Immediately behind the cab, the engine cooling system and air intake/intercooler/exhaust unit is located, in a hydraulically tiltable carrier that also houses some ancillaries and up to two spare wheels/tyres and hoist. Immediately behind this carrier, a double drum power take-off (PTO)-driven winch system capable of handling the weight of a main battle tank (MBT) can be fitted. German Army HX81s are fitted with twin 20,000 kg rated winches, with an additional self-recovery winch fitted to those with an armoured cab.

Being a tactical-role truck, NATO tow and recovery fittings are fitted front and rear, including an optional standard towing pintle on the rear cross member. A steel front bumper is standard, as are various chassis-mounted brackets for sealed-for-wading stowage options. Tactical (including blackout) lighting is part of the standard electrical specification, with further modifications to enable the installation of additional military-specific electronics and communications or command equipment an option.

The Jost fifth wheel is located over the rear tandem, and has a rated load of 19,000 kg when 16.00 R 20 tyres, as well as the IAC, double winch system, and a spare wheel are fitted. This rating increases to 21,000 kg with 24 R 21 tyres. The 840 litre aluminium fuel tank is located on the left-hand side between the front and rear axle pairs, giving a >800 km range. The chassis together with cab and all ancillaries (including all driveline components) is capable of fording to a depth of up to 750 mm without additional preparation. All external compartments are watertight as the HX range are designed for an optional 1.5 m fording depth.

The HX81 drivetrain, while consisting of commercially-available components, is specific to the HX81 and components are extensively revised for the military HET role. Motive power is provided by a MAN D2868LF04 V8, 16.16 litre diesel engine rated at EURO 5 emissions compliance. The engine is conventionally located, longitudinally between the chassis frame and under the cab. The LF04 variant of the D2868 is military-specific and is supplied without a front-mounted cooling fan, no plastic covers, military software, and the ‘anti-wear package’ to enable long-term use on low and military-grade fuels. Maximum power output is 500 kW (680 hp) at 1,900 rpm, and peak torque is 2,700 Nm at 1,000 to 1,700 rpm. The torque delivery curve is optimised to match the TC-Tronic automated gearbox and HET application. The cooling package is HX81-specific, and includes a pair of HX77 radiators mounted in parallel. The original HX81 prototype was fitted with a variant of the D2868 engine rated at EURO 3 emissions compliance and developing 660 hp (492 kW).

The ZF TC-Tronic automated constant mesh gearbox (branded TipMatic in MAN’s commercial product line) has 12 forward and two reverse gears, and is coupled to a ZF WSK 440 torque converter and (with the exception of Australia), a MAN G253 two-speed transfer case with full-time all-wheel drive. The ratio spread of the gearbox allows for the use of full engine torque at almost any speed, additionally, retardation provides 500 kW of wear-free braking for downhill descents.

The driveline of the HX81 range is completed by MAN’s single tyre specific hub-reduction axles, originally VP/VPD-09 units rated at a technically permissible 9,000 kg (each) for the front, and HPD-1372-E/HP-1342-E units rated at a technically permissible 13,000 kg (each) for the rear. Later HX81s have 11,000 kg rated front axles taken from the HX44M, and 16,000 kg rated rear axles are an option. With 16.00 R 20 tyres fitted, technical maximum rear axle loads are reduced. All axles are fitted with driver-controlled cross-axle differential locks; there are longitudinal differential locks in the rear axle combinations, and the transfer case.

Brakes are dual-circuit air-actuated drums on all axles. MAN’s Electronic Brake System (EBS) with ABS with off-road logic is standard, these supplemented by an air-actuated exhaust brake with additional Exhaust Valve Brake system. The gearbox retarder, engine braking and service brakes are automatically blended by the vehicle electronics, with a heat exchanger dissipating the waste heat into the cooling system.

The HX81 range is fitted with leaf springs on all axles. Front steer-drive axles are sprung by a combination of parabolic leaf springs with progressively acting rubber assistors and shock-absorbers, suspension rated at 10,000 kg per axle in standard configuration. Rear axles are sprung by inverted multi-leaf trapezoidal springs with radius rods and anti-roll bars, and the suspension is rated at 14,500 kg per axle in standard configuration.

Early HX81s were fitted with 395/85 R 20 tyres, although these have since been replaced by 16.00 R 20 tyres. Other options include 14.00 R 20 and 24 R 21. Tyre chains for all tyre sizes up to 16.00 R 20 are permitted. A semi-automatic or central tyre inflation system (CTIS) and run-flat inserts are optionally available.

Steering is ZF 8099 hydraulically actuated, and on trucks with 11,000 kg steer-drive axles this is uprated with each steer-drive axle featuring steering actuation on both sides. Steering lock is 36° on the front axle, and 18° on the second axle.

The HX81 is transportable by the A400M transport aircraft. Approach and departure angles of the tractor (without trailer) are 41° and 44° respectively. Gradeability of the tractor (without trailer) is in excess of 60%, and it is capable of climbing a 600 mm vertical step and crossing a 2.3 m wide ditch. The fording depth is 750 mm without additional preparation.

Shaun Connors