Acoustic warfare support measures, abbreviated AWSM, are defined in the NATO Glossary of Terms and Definitions as actions taken in an underwater environment to search for, intercept and identify radiated acoustic energy in order to exploit it. The key feature is that these measures involve no intentional underwater acoustic emission, so they are passive and generally not detectable by hostile forces. This makes them a quiet foundation of anti-submarine warfare.
Place in acoustic warfare
AWSM is the passive listening element of a larger set. Acoustic warfare countermeasures use deliberate emissions to deceive or jam, while counter-countermeasures protect friendly use of the acoustic spectrum. Support measures do the detecting and classifying without giving away the listening platform, which is why passive towed and hull-mounted sonar arrays sit at the heart of the capability. The distinction between passive listening and active emission is fundamental to how a warship stays hidden while it hunts.
Why passive detection matters
A submarine's greatest advantage is stealth, and active sonar, which pings the water, can reveal the hunter as much as the hunted. Support measures let a ship or submarine build a picture from the noise a target radiates, holding contact without announcing its own presence. Modern anti-submarine warfare therefore leans heavily on sensitive passive arrays and on the processing that turns faint radiated sound into a usable track.
How Canada acquires undersea sensing
The Royal Canadian Navy buys sonar and acoustic detection as integrated parts of major warship projects under the National Shipbuilding Strategy, managed by Public Services and Procurement Canada and set out on the federal National Shipbuilding Strategy page. The Canadian Surface Combatant carries hull-mounted and towed low-frequency active and passive sonar, as described in the RCN Canadian Surface Combatant overview.
Building the fleet
Construction of the surface combatant fleet, now the River-class destroyers, is under way, marked by a 2024 Department of National Defence announcement. Each ship is designed as a node in a wider network, which supports allied anti-submarine operations.
The interoperability link
Canadian systems are engineered for NATO interoperability rather than to a single prescriptive standard, drawing on alliance research shared through the NATO Science and Technology Organization sensing programme. For a sonar or acoustic sensor supplier, that means designing passive detection that meets the support-measures function while fitting into an allied networked warfare picture. It also means treating interoperability with allied platforms as a core requirement, not an afterthought, since Canadian ships are built to operate as part of a larger coalition force.