Submarine sensors – Keeping safe and effective beneath the waves

Role of submarine sensors

Submarines remain a vital element in today’s naval operations, a position they will continue to occupy for the foreseeable future. Maintaining the underwater vessel’s advantages, and keeping it safe in the constantly evolving “cat-and-mouse” battle with airborne and surface sub-hunters requires the continuous refinement of existing equipment and the development of new technologies.

Submarine types – Of boomers and killers

There are many different classes of submarine, from the ‘boomers’ – large boats patrolling at depth carrying nuclear-armed ballistic missiles – through to smaller ‘hunter/killers’ and general-purpose attack submarines, to ‘midget’ subs and small special forces craft.

Medium-sized subs make up a significant portion of the global submarine fleet, and traditionally these boats have been engaged in hunter/killer tasks, such as sinking other naval vessels. Although there are some indications that this kind of operation may be returning, in recent times – with the advent of better sensor systems and a change in operational emphasis – the modern medium submarine is mainly engaged in ISR (intelligence, surveillance, reconnaissance) and land attack missions.

In such operations the boats operate relatively close to hostile shores using sensors to conduct ISR, with the ability to launch conventionally-armed missiles against surface and onshore targets. With a sub on patrol, a strike response to pop-up targets can be conducted more rapidly than aerial bombardment, while a tactically-placed submarine can also lock up enemy warships in their ports and close down strategic seaways.

Today’s utility submarines also have the ability to operate in varying depths of water. For instance, the German Navy’s 212A boats are shallow-water specialists and optimised for operations in the Baltic, whereas the new 212CD boats will have true blue-water capability. Colombia’s 206s even operate in a riverine environment.

Modern sensors and their operation

Equipping submarines to safely conduct a wide range of operations across varying environments combines two interrelated requirements: to maximise operational effectiveness, and to reduce vulnerability to detection.

Keeping the boat hidden is the key to keeping it safe, yet to conduct its operations it must come up to periscope depth so that its scopes and/or mast-mounted antennas can be raised above the surface to collect data. Once the mast or scope is lifted it becomes vulnerable to detection by radar or visual means. Making masts and periscopes shorter and smaller certainly helps, but comes at the cost of the size and number of sensors that can be carried.

Other means of signature reduction involve shaping the mast/scope so that it has a low radar cross-section, as well as a reduced wake signature.

While the physical characteristics of a mast continue to be refined, a more recent trend – and the primary focus of current development – is to harness the latest digital computing technologies such as artificial intelligence (AI) to optimise imagery processing. This, in turn, minimises the length of time that the periscope/mast needs to be lifted to less than three seconds in some instances, reducing its vulnerability to detection. The ultimate aim is to gather the most information possible with the minimum amount of mast ‘lifts’.

Advancing back-end technology

Back-end processing developments also permit the submarine to operate further away from the area of interest yet retain operational effectiveness. The extension of effective sensor range also increases the chances of early threat detection, verification and validation when used to provide situational awareness for the boat, in turn allowing the submarine commander to initiate the relevant evasive tactics at a much earlier stage. The use of AI also significantly reduces workload for operators.

Modern optronic mast systems (OMS) typically contain a number of sensors working in various bands. Sensors can provide coverage in daylight and in both medium- and long-wave infrared for nighttime imaging. Recent years have seen the emergence of short-wave infrared imaging (SWIR), which is effective in hazy and foggy conditions. Laser rangefinders are used to provide additional range finding to the traditional capabilities of the optical periscope, and additional sensors such as electronic warfare receivers are usually included to detect hostile radars.While the OMS provides many advantages, not least of which being that its installation does not require the penetration of the hull and the operations room does not need to be directly below the mast, there is still a place for the traditional direct-view glass channel periscope, and HENSOLDT is the only provider actively developing new periscope technology.

“Many navies still value the familiarity of a periscope, which supports tactical operations and situational awareness of the surface environmental. And in many ways, it´s superior for range-finding, targeting and stealth operations during high contact density situations”

Jason Looper
Sales Manager at HENSOLDT and former submarine officer

Current submarines usually have two systems, with one typically employed for ISR and general situational awareness, and the other for targeting. Whether both are periscopes or OMS or a combination of both is a matter of operator preference and operational requirement. Dual OMS installations are increasing in popularity as sensor and back-end processing capabilities improve, and also due to the greater number of sensor types that can be carried. System redundancy is another benefit.

HENSOLDT developments

HENSOLDT has a very busy development programme across its range of submarine sensor products. It maintains development of its SERO range of periscope systems, and has a strong market position – notably in Asia and South America – for retrofit solutions for older submarines in either drop-in, stand-alone installations or those fully integrated for operation from a console. Development continues on the ‘front end’ of the optronic masts, which has recently seen the introduction of the OMS-150 and -300 optronic masts. The OMS-150 now incorporates SWIR capability.

“Perhaps more importantly is the work on back-end processing and new inboard equipment. This work addresses obsolescence issues and also adds new capabilities, such as improving de-hazing/de-fogging functionality within the image processing, object detection and classification capabilities.”

Andreas Häußler
System Engineer at HENSOLDT´s optronics division

HENSOLDT has also introduced a new system known as OctoEye360, which is due to become operational on Germany’s new 212CD submarines in 2026. This is an extensional system that provides additional capability to the OMS and/or periscope. Essentially a “carrier of antennas”, which may be from third-party suppliers, the OctoEye has eight fixed visual cameras and a similar number of uncooled infrared sensors, which combine to provide a stitched 360-degree image by day or night. The OctoEye can be mounted on its own mast, or on other masts, and in the 212CD is mounted on the snorkel.

Driven by a Swedish requirement for a back-up to single-scope/mast submarines, the OctoEye provides situational awareness, and is of particular use for general threat detection when snorkelling or transiting through crowded waters. The wide-area image, backed up by advanced back-end processing algorithms, provides early detection of threats or possible targets, and cues the high-power mast(s) for more detailed analysis. It also acts as an important back-up in the case of issues with the primary sensor systems, providing a robust ”get you home” capability.

In the marketplace

Through its development programme, HENSOLDT retains its position as a leading supplier of critical submarine sensor solutions, and boasts an impressive list of navies around the world as customers.

The company has seen an increase in requirements in Asia, where navies are seeking to improve their maritime capability in the face of geopolitical trends in the region.

HENSOLDT is also addressing the North American market. The US Navy part-funded development of the OMS 110 system, a low-profile optronic mast that includes SWIR capability, which has been trialled aboard the new Virginia-class fast attack submarine.

To back up its offering, HENSOLDT seeks to engage customers in long-term relationships rather than just acting as an equipment supplier. Life-cycle support is an important element of the offer, which can include the establishment of budget plans to minimise vessel down-time, and the management of upgrade programmes.

The establishment of in-country sensor workshops is another option, one that reinforces the long-term nature of HENSOLDT’s involvement with a customer.