HMCS Assiniboine and Sea King Helicopter
This photograph shows two major postwar Canadian naval technology developments: operating large helicopters from relatively small ships, and the variable depth sonar.
The square "bear trap" visible in the middle of the flight deck (centre) used a system of cables and winches to allow large helicopters like the Sea King seen here to land on relatively small warships like HMCS Assiniboine, even in rough seas. By allowing anti-submarine warfare operations to continue in virtually all types of weather, it conferred a critical military advantage. The mechanism at the ship's stern (centre right) supported, launched, and retrieved a variable depth sonar, which greatly increased the range at which submarines could be detected.
Naval Museum of Alberta