The electro-optical director – eyes of the Royal Navy fleet

Electro-optical director (EOD) mounts provide important situational awareness, visual tracking and gunnery fire control. Here we take brief look at the history and capabilities of these systems in RN service.

EODs are used to track targets within visual range using either daylight or infra-red. These cameras are a prime surveillance tool and are much relied on for short-range situational awareness. Stabilised and mounted high in the ship, the cameras feed high-resolution images to screens in the operations room and the bridge that are far better than can be obtained by the human eye using binoculars. They are an important tool for target identification, an aid for search and rescue, navigation, aircraft control and even mine avoidance. Modern systems can also track targets automatically and provide fire-control solutions to the Combat Management System and direct to weapons.


Analogue fire control systems were used aboard warships prior to the introduction of computerised systems, to control the targeting of guns with either optical or radar sighting. Early computers were used in the first semi-automated gunnery systems introduced in the 1960s. Today’s fire-control systems typically interface with radar, or the EOD that provide infra-red search and track (IRST) and laser range finding used to calculate the precise direction and distance of the target.

Sea Archer

The RN’s first EOD was the Sea Archer system which has its roots in optical aspects of the tracker developed by BAe for the Field Standard B2 variant of the Army’s Rapier surface-to-air missile system. The Army’s specification also suited the marine environment and development work had already been funded so both services benefit from spares commonality and joint financing of upgrades. Sea Archer 1 development began in 1974 by Sperry/Marconi under the name Sapphire and the original system consisted of a Marconi ST802 tracking radar, a Sperry Gyroscope gunnery Predictor based on the 1412 computer and special interfaces for the Vickers Mk8 4.5 inch naval gun. The first successful live firing trials of a computerised gunnery system was conducted in 1975 at HMS Cambridge (RN gunnery school near Plymouth, closed in 2001).

Sea Archer 1 first went to sea in 1983 with the Peacock class Hong Kong patrol ships. Officially designed GSA.7, the mount provided fire-control for the Oto Melara 76mm gun. In 1982 BAe began development of an entirely new version called General Purpose Electro-Optic Director (GPEOD). Utilising the distinctive ball shape, this was the basis of the Sea Archer 3 system ordered by the RN in 1985 designated GSA.8. Two mounts were fitted to each of the batch III Type 22 frigates and together with radar or manual inputs, provided fire-control for the 4.5” guns. When HMS Cornwall entered service in 1989, she was the first major RN combatant to have a fully autonomous digital fire control system and first to have thermal imaging sights. A single GSA.8 Sea Archer mount was also fitted to the Type 23 frigates and continues in service today.

  • Sea Archer Type 23 Frigate

    “Pacman” The Sea Archer seen here on the foremast of HMS Kent provides inputs for fire-control of the 4.5″ Mod 1 medium calibre gun. Each system cost around £2.2 Million at 2001 prices. Including below decks equipment, it weighs 585Kg.

  • Sea Archer Type 22 Frigate

    Twin Sea Archer GSA.8 EODs, HMS Cornwall 1989.

  • Rapier Field Standard C

    The EOD on the Army’s Rapier Field Standard C mount – originally developed in the 1970s and the basis for the RN’s GSA.8 Sea Archer.

  • Early days – the RN’s first EOD – the GSA.7 can be seen on the bridge roof of HMS Peacock. (Alongside in Hong Kong, 1987)

Sea Eagle

Besides the legacy Sea Archer there are two other EOD types in service with the RN’s Surface ships. The Ultra Electronics 2500 series is fitted to the Type 45 destroyers and the QEC Carriers but the most numerous mount is the Chess Dynamics FCEO, part of Sea Eagle family of systems. FCEO is fitted to the Type 23 frigates (2 mounts), the batch II OPvs (1 mount), some RFAs and is going to be fitted to the QEC aircraft carriers (4 mounts). The Sea Eagle FCEO electro-optical fire control director is potentially capable of controlling any naval gun from 30mm to 127mm, for fire against air, surface and shore targets. In RN service it is the integrated fire control system for the DSI 30mm Automated Small Caliber Guns (ASCG) which equip these vessels, with one director mount for each cannon.

The Sea Eagle is based on the T-shaped Iota chassis specifically developed by CD as a platform for high-accuracy optical systems in demanding environments. The Iota carries a Leonardo SLX Hawk high resolution mid-wave thermal imager, a Piranha-36 colour TV camera and a Hensoldt LP eye-safe laser rangefinder. The director mount can slew rapidly and smoothly to track fast-moving targets either when tracking automatically or under line-of-sight gyro control. Incorporating automatic target acquisition and tracking, and automated slewing to search radar contact indications, the Sea Eagle FCEO helps reduce the operational burden on crew. The system uses sophisticated image processing techniques to enhance target tracking and ballistic prediction and includes with compensation for meteorological effects which increases overall gunnery accuracy. The system also captures target snapshot images to record points of interest automatically for post-action review and training purposes.

Sea Eagle is designed to be operated as a fully integrated element of the multi-function console-based combat systems fitted in RN warships, but may also be controlled through a dedicated standalone console on the bridge. The director mount is relatively small and light in order to minimise topweight and makes it suitable for fitting to small vessels. The cameras are modular and can be easily swapped out for maintenance or replaced with upgraded versions.


3 EO Mounts Ultra 2500 Sea Eagle Mirador

Modern Royal Navy EOD Mounts – (Left) the Ultra Electronics 2500, (Centre) Chess Dynamics Sea Eagle FCEO and (Right) Thales Mirador Mk2 which is likely to equip the Type 31 frigate.

Chess Dynamics, based in Horsham in Sussex has recently been awarded a contract to provide 3 FCEO mounts for each of the Type 26 frigates. Two mounts will be used to control the two 30mm ASCGs while a third mount will provide part of the fire-control solution for the 127mm Mark 45 Mod 4 gun. CD is also hopeful of winning orders for the Australian Hunter class frigates. EO camera technology continues to evolve and the company is working to develop cameras that use AI-assisted image recognition to help automatically distinguish between targets.

The UAS threat is increasing both at sea and ashore and CD is incorporating C-UAS technologies into its new naval mounts based on those already proven within land military operations and at large commercial airports. After the drone incident at Gatwick airport in December 2018, CD was contracted to provide C-UAS equipment. These have the capability to automatically detect and track targets and can be integrated with kinetic or non-kinetic systems to defeat drones. Typically radar is used to make the initial detection of the drone which then cues the TV or IR camera onto the target when in visual range. The operator can then neutralise the drone using either electronic jamming, a laser dazzler or a gun firing airburst ammunition.

  • The two Ultra 2500 EODs carried on the bridge roof of the Type 45 Destroyers provide fire-control solutions to the 4.5″ gun below.

  • EOD Mounts HMS Queen Elizabeth

    All round coverage – the position of EODs on HMS Queen Elizabeth. The 3 Ultra 2500 mounts are shown in the square boxes and the 4 Sea Eagle positions are circled, one adjacent to each of the 30mm ASCGs (not yet fitted when this was taken in September 2019).

  • One of the three Ultra 2400 series mounts fitted to the QEC aircraft carriers.

  • Showing the arrangement of the three main internal elements – thermal imaging camera, daylight TV camera and laser rangefinder.

  • The principal Sea Eagle FCEO components. The camera has a 36x optical zoom. The thermal imaging camera provides passive Mid Waveband Infra-Red (MWIR) imaging in day, night and poor visibility. The Laser Range Finder can measure distances accurately out to around 10km.

  • This is an example of what an operator might see on screen in the ops room or bridge. The main display shows the thermal image and the DLTV image is bottom right. A person on the shoreline is being automatically tracked (denoted by the green box)

  • FCEO Sea Eagle Type 23 frigate

    One of the two FCEO Sea Eagle mounts carried by the Type 23 frigates on port and starboard pedestals amidships. The optical designator can be seen behind which provides an alternative manual way to indicate targets to the weapon systems.

  • The single FCEO mount carried by the batch II OPVs

Ultra 2500

Although slightly larger and older, the Ultra 2500 series mounts have similar features and capabilities as the Sea Eagle. As well a directing the 30mm cannons on the Type 45 destroyers, they also form part of the GSA.9 system that controls the 4.5″ gun. Babcock provides in-service support for the GSA.9 to the RN and recently awarded Ultra a 3-year contract with a potential two-year extension to maintain the EOD systems. Three 2400 mounts are currently fitted to the QEC carriers to give 360º coverage and are primarily used for general surveillance, tracking of the ship’s own aircraft and glide path monitoring, providing imagery to flyco, the ops room and bridge. (4 additional Sea Eagle mounts will be fitted to HMS Queen Elizabeth along with the four 30mm cannons in the near future).

Because Thales is the systems integrator and provider of much of the communications and sensor equipment for the Type 31, it is likely that their Mirador Mk2 EOD will be selected for the frigate. At 220kg, the Mirador mount is slightly larger and heavier than both the CD and Ultra products but is already in service with 10 navies worldwide. In the air, both the RN’s Merlin and Wildcat make use of smaller and lighter EO/IR mounts for surveillance and targeting. The L3 Wescam MX15-Di will provide laser guidance for the Martlet missiles fired by the Wildcat helicopter.


While radars may be more immediately obvious to the casual observer, the electro-optical directors are a critical part of the sensor fit of the modern warship, and especially when operating on complex littoral environments.