I was going to say exactly the same thing.
Do you know how much is an Aegis cruiser? $2 billion
The Tomahawk is good in terms of range (and right there US will not sell it to VN because it violates the 300 km range limit as per arms treaty limitations). But other than range, there is nothing special there, its actually old technology. Russia, China and India already went further than the tomahawk.
What you really want is the Brahmos (match 2.8 speed), and a little bit later, the Brahmos M (match 3.5 speed). The M in Brahmos M stands for mini, the Brahmos is actually a big missile (about 9 meters long) and is heavy, so SU-30 can't carry it unless there is structural modifications of the airframe (India is getting that in the new SU-30SM's so that they can carry the missile), so they decided to make an smaller version, 6.5 meters long and lighter so it can be carried in many platforms. They are testing the missile now. SU-30MK2 can carry 3 Brahmos M missiles. Range is 300 km.
With an speed of match 3.5, its very, very difficult to stop that missile, speed is the key factor in anti ship missiles. Subsonic missiles are easy to intercept, but supersonic is not easy at all, ships detect the missiles when they are already too close, before the ship's missile defenses have time to react.
That's why VN should not get into sophisticated, expensive surface ships, those ships would not be able to survive, they'll get destroyed by chinese cruise missiles (including supersonic cruise missiles) fired from stand off range from multiple launch platforms including HK-6 bombers. VN needs to concentrate in submarines and small, cheap surface ships at this point.
Any ship, including Aegis cruisers, can be overwhelmed by saturation missile attacks.
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