The Thales Watchkeeper is an unmanned aerial vehicle (UAV) for intelligence, surveillance, target acquisition and reconnaissance (ISTAR), and is the latest, and most capable and sophisticated, unmanned aerial system (UAS) in the British Army. MS&T’s Dim Jones visited the UK’s Watchkeeper Force and 47th Regiment, Royal Artillery at their bases at Boscombe Down and Larkhill.

Watchkeeper (WK) is a strip-launched tactical UAS, whose mission is: “to support Force Elements at High Readiness for Responsive tasks in order to succeed on future operations. Force Prep priorities are the provision of Aviation FIND capability to 3 (UK) Division and the Joint Expeditionary Force.” In order to do this, WK needs to be able to deploy wherever the Army goes, to operate in contested airspace, and to be robust against peer and near-peer threats to the air vehicle and its communications.

WK Force HQ is co-located with UK Army HQ in Andover, but the force is part of the Joint Helicopter Command (JHC). Contract Award was in 2005 with flying operations commencing 2014, at which time the UK was engaged in Operation HERRICK (Afghanistan). It was in this theatre that initial WK operations were conducted from Camp Bastion by 32 and 47 Regiments of the Royal Artillery. Concurrently, the UK element was based at Boscombe Down, as part of 1 ISR Brigade.

In 2016, following the cessation of HERRICK, the force, now 47 Regt only and part of JHC, deployed to Ascension Island in the South Atlantic, to generate new WK pilots. Meanwhile, Operational Test and Evaluation (OT&E) work, and some Army training, was conducted by Thales at West Wales (Aberporth) Airport. In 2018, Equipment Standard 2 (ES2) was delivered and in 2019, elements of the force deployed to RAF Akrotiri in Cyprus to continue training, where a detachment remains.

The Watchkeeper System

WK is a step change in the Army’s employment of UAS, in that previous systems have been focused on Deep Fire Targeting for the artillery, whereas WK is an ISTAR asset. The components of the system are: the UAV itself, which is a derivative of the Elbit Hermes 450, which the Army previously operated; the Ground Control Station (GCS) and associated equipment; and the Groundcrew Detachment.

The aircraft is of composite construction, has a wingspan of 10.8m (35.4ft), a length of 6.5m (21.3ft) and a gross weight of 500Kg (1100lb). It has a maximum line-of-sight (LOS) range of 150km, which can be extended by the use of a relay GCS, a technique known as ‘daisychaining’, theoretically unlimited but in reality constrained by aircraft range and the availability of landing sites. Its maximum speed is 85kts, and endurance 14hrs from 100kg of fuel, all carried in the fuselage. The maximum altitude is 16,000ft, and it can operate from either paved surfaces or prepared rough or grass strips, needing a minimum of 650m.

ES2, besides software changes, introduced an airframe anti-icing system. Continuous flight in icing conditions is not however cleared, nor are operations in heavy rain, hail, ice, snow or towering cloud. The aircraft can operate happily in non-convective cloud. The maximum wind speed for take-off and landing is 25 kts, with crosswind at 15kts and tailwind at 5kts.

Ground equipment comprises: an Automatic Take-Off and Landing System (ATOLS); a GPS Take-Off and Landing System (GTOLS); Ground Beacon Unit and Ground Radar Unit, which interact with equipment in the aircraft; wide- and narrow-band datalink (DL), collectively known as the Ground Data Terminal (GDT); and a landing arrestor system with two separate 50m span cables. The wide-band DL is Line-of-Sight (LOS) and carries sensor data; the narrow-band is omnidirectional, but for aircraft control only. A Flight Line Support Command Unit (FLSCU), a modified Pinzgauer vehicle equipped with a starter power supply and Portable Aircraft Test Equipment (PATE), is also used to tow the air vehicle. The entire suite is air-portable; two A400M Atlas aircraft can carry a package comprising two WK aircraft, a GCS, an FLSCU with support spares and tools, and image analysis equipment.

The eight-man groundcrew team comprises a detachment commander, a PATE operator, an arrestor specialist, four operators and a driver. The GCS, which can be sited up to a kilometre away from the launch and landing point, has two identical and interchangeable operator stations for the aircraft captain and payload operator. The comms suite includes Bowman Data and Voice, and a Lightweight Multi-Band Air Radio (LMAR), which is used for both ground and air comms. LMAR provides voice comms with manned airborne assets such as Apache and can relay with ground forces out to 150km. The comms equipment is supported by a signaller, and the GCS can also accommodate an Intelligence Analyst and a Mission Commander.

The UAV is equipped with twin sensors, an Elop Compass IV Electro-Optical/Infra-Red (EO/IR) system, with a Laser Sub-System (LSS), and a Thales I-Master dual-mode Synthetic Aperture Radar (SAR) with Ground Moving Target Indicator (GMTI). Trials are currently being conducted on a maritime (MMTI) capability. The EO/IR is mounted underneath the rear fuselage, and the SAR under the forward fuselage. Only one sensor can be used at a time but concurrent operation may be possible in future.

Servicing the Watchkeeper UAV using the Portable Aircraft Test Equipment (PATE). Image credit: Thales.

Operating Watchkeeper

The WK operation starts with ground preparation (about 40 minutes), followed by a tow to the engine starting point, where the Wankel engine is fired up. The aircraft is then towed to the take-off point by the groundcrew and prepared for launch. Air traffic clearances are sought and acknowledged and when cleared, the aircraft can take off automatically under the GCS control. Unlike other large UASs (e.g. Predator) the pilot has no direct control over the aircraft  as it operates autonomously to a set programme. Changes can be made however, via the GCS computers. The flight profile is monitored by the crew through the twin flat-screens and the Air Vehicle Display Computer (AVDC) in each GCS control position; the AVDC is the primary control means during take-off and landing, and the back-up system in flight. The joystick is used only to control the sensors. The primary aircraft recovery mode is ATOLS, with GTOLS as a back-up. If for any reason the landing profile is not satisfactory, the aircraft is programmed to go around, or can be commanded to do so. The approach profile is designed to take the first of the two cables, which is set 50m from the threshold of the runway; the second is a further 50m inset; if it fails to pick up the first cable, the engine will be cut.

Should the engine fail in flight for whatever reason, it cannot be restarted, and the aircraft will have to be recovered, preferably to its Main Operating Base (MOB). The engine-out glide ratio is about 4km (2.5 miles) per 1000ft, giving it a glide range of about 64km (40 miles) from its maximum operating altitude to a destination at sea level. As part of the mission planning process, emergency profiles (using GTOLS) are programmed for each surveyed landing site; if the aircraft cannot reach any surveyed site, it will fly to crash-land in a safe area. Similarly, if the datalink command system is lost, the aircraft will fly to a designated safe area. Watchkeeper has a transponder transmit facility, and so will appear on another aircraft’s suitably equipped TCAS system, but it has no receive facility and no detect-and-avoid system. It is, therefore, not permitted to fly in Class G (unrestricted) airspace and, although it is certified to fly in controlled airspace, the presence of Class G underneath most of the controlled airspace effectively limits Watchkeeper to segregated airspace, either permanent (such as the Salisbury Plain danger areas), or temporarily NOTAM’d.

Pilot's control position in the GCS (AVDC are the small screens at the bottom, Comms equipment at the top). Image credit: Thales.


So much for the WK system itself – how does one get to be a part of it? Firstly, recruitment; nearly everyone wishing to join the WK team must start by applying for and joining the Royal Artillery, although there are avenues whereby suitably qualified people in other branches can apply to transfer. In the case of pilots (both crew members are qualified pilots), the minimum rank for training as a pilot is Lance-Bombardier, and the minimum for aircraft captain is Bombardier. This means that aspiring NCO pilots will go through their initial training and early service as Gunners and, although it is possible that a person may be eligible for promotion and UAS conversion on completion of basic training, it is more likely they will serve at least two years as a Gunner before going before an internal WK selection panel. Ab-initio officers will also join the RA through the Royal Military Academy Sandhurst but may be selected for UAS training as part of that process. In both cases, candidates will undergo bespoke UAS aptitude testing at the Officers and Aircrew Selection Centre at RAF Cranwell.


The WK Force has a purpose-built training facility, constructed and operated by Thales, at the RA HQ at Larkhill, only a few miles from Boscombe Down. There are separate classrooms for operators and maintainers, who undergo a parallel course. The operator classrooms comprise two instructor workstations, each with a CBT console and a GCS console simulator, and 16 operator workstations, similarly equipped. The maintainer classroom comprises one instructor workstation and eight CBT consoles, and can also be used for task training such as launch and recovery. The instructor cadre is a mix of Thales (almost all ex-military) and serving military. The operator training process, through which all pilot candidates pass, comprises: a foundation course; an Airmanship Development Flying Module (ADFM); a 50%/50% mix of classroom Computer-Based Training and Computer-Aided Instruction (CBT/CAI); Individual practical training in part-task trainers (PTT); team training and practice in full-task trainers (FTT) and Emergency Procedures Trainers (EPT); and live flying – practical training with deployable equipment.

The pre-requisite training (UAS Level 1), which imparts all the knowledge and experience needed to embark on the formal course, is a generic delivered UAS Operator’s course, and embraces a UAS overview, an introduction to UAV operation, airmanship, flight safety and ground handling. The ADFM gives the student nine hours of live hands-on flying, performing profiles similar to those of a UAV, and learning how an aircraft works. The Level 2 course encompasses instruction in: meteorology; Intelligence Preparation of the Battlefield (IPB) and targeting; airspace management; airfields and Rules of the Air; aviation regulations (through the Military Aviation Regulations Document Set (MARDS) and airworthiness); advanced airmanship and flight safety, including occurrence reporting; Air Traffic Control (ATC) procedures and Mission Planning; and tactical employment and operations. The instruction and classroom simulation phase lasts approximately six weeks, culminating in a six-hour practical ‘Intermediate Handling Test’ and progression to the advanced simulation and live flying phase.

Students, both operator and maintainer, gain practical knowledge of the WK system in the PTT Hall, which contains a demonstration mock-up, comprising: a sectioned air vehicle and sensors, connected to a PATE set and with additional sectioned engine; full ATOLS/GTOLS, datalink, and arrestor equipment; and an air vehicle container, positioned on an airfield plan showing the equipment disposition. All components are modified to the latest aircraft standard. There is also an aircraft container, in which the dismantled aircraft can be stowed.


The FTT Simulation Hall contains three GCS and two tactical party (Tac Pty) simulators, all constructed to a high level of fidelity by the manufacturers of the deployable equipment. There is an adjoining simulation control booth, and a briefing room in which After-Action Reviews can also take place. The Level D compatible GCS simulators can be individually configured or grouped in multiple ‘role’ simulations, allowing operators to interact in single or multiple simulated mission scenarios involving up to three UAVs simultaneously. There are three FTT databases, supplied by Presagis and responsive to EO/IR and SAR: a high-fidelity 200 x 200km2 terrain database of the UK, with selected areas in 3D; a 160 x 160km2 terrain database of Afghanistan; and a 70 x 70km2 database around Aberporth. These can be populated by 300+ entities. Although the focus is now on expeditionary rather than theatre ops the mix of scenarios satisfies the required training and new databases can be imported. All elements of an FTT training session – flight controls, payload, voice and message comms and physical reactions - are recorded for AAR, and instructor can flag key events either as they happen, or after the mission. At present, emergency procedures can only be practised in a separate EPT.

As in many other areas of flight training, the live/synthetic mix generates vigorous discussion, but there are aspects of UAS ops which influence the debate. By its very nature, the fidelity of, and immersion generated by, a GCS simulator are extremely high – in essence, the operators ply their trade in a simulator environment, and there are no physiological issues – such as motion - to be replicated; environmental factors, such as noise and heat – can be introduced if required. However, the friction generated during a live operational UAS mission, such as dealing with ATC and other ground agencies, and the adrenalin associated with risk, are real and, although they may not be as physical as in manned aircraft ops, they are there.

Live training currently takes place at Boscombe Down, Akrotiri and Aberporth. Image credit: Thales.

Live Training

Similarly, although WK is unarmed and the pressures of correct target identification may not be as direct as for an armed UAV engaging the target itself, they are also there. These factors militate for a significant level of live training, as does the fact that the ground agencies and the support parties also need live training. Finally, the relatively low cost of live UAS operations reduces the budgetary pressure in comparison with modern fast-jet manned ops. In counterbalance, the airspace and scenario constraints on live UAS ops in the UK make synthetic training a crucial part of the mix. The current live/synthetic ratio for the ab-initio course is in the WK force is 68%/32%. The balance to meet currency requirements for qualified pilots is harder to quantify, but the minimum live and synthetic hours over a three-month rolling period are 7.5 and 10 respectively.

Live training currently takes place at Boscombe Down, Akrotiri and Aberporth. At Boscombe Down, the aircraft operate from the parallel taxiway, thus leaving the main runway clear for other aircraft, which can trample the de-tensioned arrestor cables. Safety rules at Akrotiri, however, mean that WK has to use the main runway, and this can deny it to other aircraft for periods of up to 1hr 40min. At Aberporth, there are two grass strips in addition to the paved runway. Conversion to Role (CTR) training in the UK focuses on support of ground units exercising in the Salisbury Plain Training Area (SPTA), and on integration with other air users, with a secondary aim of supporting other agencies and generating a wider awareness of the system and its capabilities.

Novel and Complex

WK ES2 has received a Release to Service from the Military Aviation Authority (MAA), and the WK force has declared Full Operational Capability (FOC). For the future, the MMTI capability is expected soon, and there is an ongoing software upgrade programme. The functions of the FTT and the EPT will be combined in a new FMS, the first of which will come on line in May this year and will greatly enhance the synthetic training which Thales is able to deliver.

The early years of the WK programme have not been without incident; five air vehicles have been lost in a four-year period, four at Aberporth and one at Boscombe Down. The causes have been various, but two themes have emerged: first, the complexity of the system – this is cutting-edge technology; and second, the high workload of the operators.

In commenting on the results of the enquiry into the fourth accident, the Director-General of the Defence Safety Authority, Lt Gen Richard Felton, observed that: “WK is largely crewed by NCOs from the Royal Artillery, whose selection and assurance is set for them to operate at a level below that for pilots of manned aircraft. Yet the plethora and complexity of information available to them would challenge the most competent manned-aircraft pilot. Here I refer to the high rate of Warnings, Cautions and Advisory (WCA) notifications, which can increase crew workload to unacceptable levels, increase the likelihood of error and can serve more to distract — WK's Flight Reference Cards (FRC) comprise 265 pages compared to the Wildcat AH1's 80 pages!”

And“…although WK's track record does not make for good reading, it's appropriate to place the accidents it has had within the broader context of the development of fully automated systems. There is much that is still novel in complex fully automated systems, especially those with advanced technology, designed to operate towards the boundaries defined by extant regulatory regimes.”

In both of these areas, the very highest standards of live, synthetic and academic training are essential, for the technical understanding of complex systems and for the high-workload management of the mission and the air vehicle, especially when things go awry. The WK Force are confident that the appropriate lessons have been learned from past experience, and action taken. The Larkhill training facility will continue to underpin the drive to maintain Watchkeeper as a safe and operationally effective ISTAR asset for UK armed forces.