Original sentence: It was there that Patriot was first regarded as a successful ABM system and proof that ballistic missile defense was indeed possible.The complete study on its effectiveness remains classified
Edited sentence: It was there that Patriot was first regarded but not very successful ABM system and proof that patriot can't intercept effectively old SCUD missiles.That was proven by many sources ,and the clear facts:The city of Tel Aviv was a target for missile strikes many many times, and patriots were not able to protect it.The complete study on its effectiveness remains classified for a while.The missile strike on Dharhan base when  the patriot fails to intercept SCUD missile confirm and proof that that old soviet made export variants of SCUD ballistic missile were not  vulnerable to Patriots.The real effectiveness of Patriot against ballistic missiles is around 30%