For over half a century, nations with diesel-electric submarines have been trying to develop an effective SLAAM (Sub Launched Anti-Aircraft Missile) that could be used as an IDAS (Interactive Defense and Attack System) against anti-submarine helicopters and low flying maritime patrol aircraft. The patrol aircraft can use a sensor that detects metallic objects (like subs) close to the surface while the helicopters can hover and use their dipping sonar suspended from the helicopter by a cable. The aircraft can drop depth charges and both aircraft and helicopters carry anti-submarine torpedoes. Until recently SLAAM systems were not deployable quickly enough or using accurate enough missiles to make them worthwhile.
Germany took these key problems on and appears to have a solution that involves an IDAS using a waterproof IRIS-T air-to-air missile. The IRIS-T has been in service on aircraft since 2005 and is an 87.4 kg (193 pound), 127mm diameter missile that is 2.94 meters (9.6 feet long). The IDAS version is a 180mm missile weighing 140 kg with a 20 kg warhead. The modified IRIS-T is very quick and maneuverable with a heat-seeking warhead that can detect any part of an aircraft, not just the engines. The rocket motor for the IRIS-T SLAAM propels the missile at subsonic speed, which is about a quarter the speed of the air-t0-air version. IRIS-T also has a proximity fuze that will detonate the fragmentation warhead if the missile is close enough to an aircraft. When used as a SLAAM it has a range of 20 kilometers. IRIS-T SLAAM can also be used against small ships and land targets because it includes a thin fiber optic cable that enables someone on the submarine to select a target soon after the missile reaches the surface and ignites its rocket motor. Four IRIS-T SLAAMs are stored and launched from one torpedo size canister which is loaded into a torpedo type that allows for a link between the sub and the fiber optic controller in the sub.
IRIS-T leaves the torpedo tube silently and does not ignite its rocket until it is near the surface. Passive (listen only) sonar on subs enable detecting the range and direction of a hovering helicopter and this is programmed into the IRIS-T so that it heads for the helicopter as soon as it reaches the surface.
IRIS-T IDAS was successfully flight tested in 2006 and the first successful test launch against a target was in 2008 with more such launches in 2015, 2016 and 2018. While this IDAS works, no one has put it into service. IRIS-T SLAAM solves the problem of making the sub more vulnerable when used. Older SLAAM designs revealed a sub’s location before missile launch. IRIS-T is more expensive and subs using it require modifications. Diesel-electric sub manufacturers have found that a cheaper solution is AIP (Air Independent Propulsion) and improved passive sensors which makes the submerged sub more difficult to detect.