and as far as i know,
brahmos does not fly ALWAYS at 2.8 or 3 mach,
right, it flies at top speed only when its required, which is most of the time.
it needs to climb up to a certain height before it approaches maximum speed,hence it makes itself easier target to be detected and intercepted,
Theres a wide misunderstanding that BrahMos cannot terrain-hug, which is false. it can terrainhug as
well as tomahawk and thats why it can sneak up to targets behind hills without exposing to lines of
fire and take out the target. (especially the block-III)
BrahMos' speed is judged by the
terrain its flying though, in plains & desert consitions (and most
other terrain in Indo-pak border) envisages lesser maneuverability required to stay agile and steer
off obsticles, therefore its possible for BrahMos to reach upto 2.5 mach or above in terrain hugging mode.
in hilly terrain (like in Indo-china border) it requires to be agile enough to skim though hills, valleys
and other such terrain obsticles and formations to reach the target, speed needs to be lessened if to
stay agile enough, but for advanced block-3, it can terrain hug even in such terrain at upto 2.5-2.6 mach
without much trouble.
secondly, its not a matter of detection but how quickly you can react to the incoming missile to prepare
countermeasures or defense systems, the faster the missile, the lesser time you have to do that, and
therefore higher kill probability for the missile is achieved.
sub sonic can fly very close to surface,hence they are difficult to detect,
This was relevent in 80s but not much now. AWACS can see them, Aerostats can see them, even
powerful fighter radars in look-down mode can see them, they dont remain stealthy anymore.
Due to their speed of 0.8 mach (the speed of a commercial airliner), it gives the opponent a lot
of time to decide what to do and how to do it. thats what matters, unless your employing something
like a SCALP/Storm Shadow missile that has very low RCS and is really difficult to detect with radar