Typical sensors include compasses, depth sensors, sidescan and other sonars, magnetometers, thermistors and conductivity probes. Radars and sonars are mostly used for military applications. This is a sonar designed to detect and locate the transmissions from hostile active sonars. Nine of the NHIndustries NH90 helicopters are equipped with sonars and radars for anti-submarine warfare. The frequencies of sonars range from infrasonic to above a megahertz. These are called towed arrays (linear) or variable depth sonars (VDS) with 2/3D arrays. Both the Royal Navy and the U.S. Navy fitted their destroyers with active sonars. There are often upward-looking under-ice sonars as well as depth sounders. The mobile base has two sonars, six lasers, three bumper sensors, and a gyroscope. This gave the vessels an ASW capability, with improved sonars and torpedo tubes. The earliest side-scan sonars used a single conical-beam transducer. Because of the problems of ship noise, towed sonars are also used. HSLs carry SIMRAD high-frequency active hull-mounted and side scan sonars. Most MCM sonars are hull mounted but a few types are VDS design. Japanese WW2 sonars operated at a range of frequencies.