A subsonic missile is better than a supersonic missile in sea-skimming ability because unlike supersonic Ashm, a subsonic Ashm won't create the sonic wave that will interfere with the water surface. Even the old Exocet can do sea skimming just 1 meter above the sea surface.
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India has Nirbhay, which is the Indian analogue to the American Tomahawk, Russian Kalibr, it is a subsonic missile. Brahmos is supersonic and can travel in excess of mach 3 speeds, though Brahmos can travel very fast which in theory can give it's target less time to take counter measures, an incoming brahmos will be very easy to detect because it would be easy for a radar to distinguish it from the background sea clutter.
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