I have been following this thread recently. As a retired Lockheed
engineer who did performance studies on THAAD, I can clear up a few
things.

1. THAAD is not currently an anti-ICBM system. It does not have the
performance (except on a lucky shot) to shoot down ICBMs consistently.
They travel too fast for THAAD's performance envelope. Specific numbers
would be classified.

2. THAAD had some development problems. They did not have even the
second team working on the original design. It appeared that a lot of
the design was made by people who had not taken "Missile Design 101." A
lot of the problems were simply stupid design and manufacturing errors.
We can only hope that those problems have been cleared up.

3. THAAD should be an effective TBM defense. That is what it is designed
for, and simulations show that it can hit a variety of targets.

4. An anti-ICBM missile would be a completely new, much larger design,
which would probably use only the basic interceptor technology, not the
same hardware.