Nowadays, anti-submarine warfare (ASW) is mainly carried out by airborne units -– mostly helicopters equipped with dipping sonar and lightweight torpedoes. Submarines remain vulnerable to these threats. Usually, the only available option is to hide at greater depths or even leave the area of operations. Especially when restricted by coastal or shallow waters, differing salt content or temperatures, this typical avoidance of detection is frequently not an option. The mere presence of an airborne ASW unit already limits the submarine's operational options. That is why Diehl Defence and thyssenkrupp Marine Systems cooperated in the IDAS Consortium to develop the IDAS weapon system -– Interactive Defense and Attack System for Submarines – to enable a submerged submarine to actively defend itself against airborne ASW threats.
The presence of an ASW helicopter in the area of operations is most likely to be detected by optical or electro-optical sensors or through receiving acoustic indicators, such as sonar intercepts of the dipping sonar. As soon as the crew detects such a threat, IDAS is prepared for operation. Range and bearing are determined by the submarine's sensor and sensor data fusion system. As soon as the operational situation is assessed as a critical defense situation, the effector is launched. For engagement purposes it is not necessary for the submarine to risk further detection by showing mast-mounted optical or electronic support measure (ESM) sensors or even by surfacing.
Fig. 1: Operational concept behind IDAS
During the underwater flight phase, the missile maneuvers in the direction of the target, breaks the surface, accelerates to cruising speed, and flies towards the target area. The operator onboard the submarine stays in full control of the missile -– “human in the loop” – while the submarine remains hidden. This is to give to the operator the chance to change the target or abort the mission. In the unlikely event of the connection being loss (optical fiber rupture) the missile will continue to operate in accordance with the operational settings, i.e. engagement of the last selected or the most probable target or mission-abort if this is in line with the rules of engagement.
Additionally, the “human in the loop” enables the system to fulfill a secondary role: engagement of surface targets where a heavyweight torpedo is not appropriate. This also provides the submarine’s commander with a means of escalation that is appropriate to the concrete operational situation. Furthermore, the integration of a GPS sensor would even incorporate land targets (e.g. to support SOF operations) into the IDAS target set.
After the IDAS program was halted in 2010, the German industry partners decided to continue with industry funding. In order to initiate the industrial development program the IDAS Consortium needed a set of requirements, which were established in cooperation with submariners of the German and other navies and laid down in a document forming part of the consortium agreement. The top-level requirements included:
The IDAS system uses an ejection container to store four missiles and eject them separately out of a torpedo tube. A thrust piston system, which is fully integrated into the container, is used to eject the missile. The ejection container has the main dimensions and weight of a typical heavyweight torpedo. This allows for easy integration into new submarine building projects as well as refits of existing submarines.
2: Embarking of an IDAS ejection container
Every IDAS missile is equipped with an optical fiber bobbin located in the missile's aft section and connecting the effector with the operator. Wings and fins are folded alongside the missile when stored and are unfolded at a safe distance from the submarine after ejection. With a 20 kg warhead and a cruising speed of more than 200 m/s the IDAS missile is capable of very effectively engaging an ASW helicopter. The whole system is pressure-proof at depths significantly deeper than periscope depth.
Fig. 3: IDAS missile components
The IDAS Consortium was founded in 2012 by Diehl Defence (formerly Diehl BGT Defence) and thyssenkrupp Marine Systems. Together with our partners Nammo and Roketsan we commenced the initial development phase in 2012 to develop a missile system that complies with those top-level requirements.
Fig. 4: IDAS Consortium and partners
The initial ejection tests were performed in May 2015 at the thyssenkrupp Marine Systems dockyard. After numerous unwinding tests with the optical fiber bobbin under varying conditions, including an ignited rocket motor, preparations were made for further tests with Norwegian submarines. In 2016 first system loading and unloading tests and then missile ejection tests from HNoMS Uredd were accomplished successfully. The initial development phase was completed by an engineering development firing test carried out in cooperation with the Royal Norwegian Navy. Thus the entire operational concept had been confirmed.
The IDAS Consortium and its international partners will achieve series production maturity for the IDAS system during the system qualification phase, in which the remaining detail development, verification and qualification work will be carried out. This phase is due to be completed and IDAS placed on the market in 2022.
For the first time in submarine operations, IDAS provides submarines with the capability to defend themselves effectively against airborne threats – without risking self-exposure. IDAS can be integrated into new submarine designs as well as existing systems. The principle of permanent missile control vi the "human in the loop" concept in combination with a submarine operational depth significantly deeper than periscope depth is an entirely new development in the execution of maritime operations. On the one hand, the operating unit does not need to risk exposure if it decides to defend itself; on the other hand, the risk of interference to the system is reduced to a minimum. IDAS will massively change the paradigms of submarine and antisubmarine operations.