Original sentence: Each phase offers different advantages and disadvantages to a missile defense system, thus the layered defense approach concept should improve overall defense effectiveness.It has been described as hitting a bullet with a bullet - a capability that has been successfully demonstrated in test after test.MDA divides its systems into 3 categories, boost phase, mid-course phase and terminal phase, each corresponding to a different phase of the threat ballistic missile flight regime.Missile defense systems being developed and tested by MDA are primarily based on hit-to-kill  technology.Our programmatic strategy is to develop, rigorously test, and continuously evaluate production, deployment and operational alternatives for the ballistic missile defense system.See National Missile Defense for the history of DoD missile defense programs.The Missile Defense Agency is the section of the United States government's Department of Defense responsible for developing a layered defense against ballistic missiles.To the surprise of the US, Canada announced in February 2005 that it will not participate in the US ballistic missile defense system (see National Missile Defense in Canada).Using complementary interceptors, land-,  sea-, air- and space-based sensors, and battle  management command and control systems, the planned missile defense system will be able to engage all classes and ranges of ballistic  missile threats
Edited sentence: Each phase offers different advantages and disadvantages to a missile defense system, thus the layered defense approach concept should improve over-all defense effectiveness.It has been described as hitting  a bullet with a bullet - a capability that  has been successfully demonstrated in test  after test.MDA divides their systems into 3 categories, boost phase, mid-course phase, and terminal phase, each corresponding to a different phase of the threat ballistic missile flight regime.Missile defense systems being developed  and tested by MDA are primarily based on hit-to-kill  technology.Our programmatic strategy  is to develop, rigorously test, and continuously  evaluate production, deployment and operational  alternatives for the ballistic missile defense  system.See National_Missile_Defense for the history of DoD missile defense programs.The US Missile Defense Agency is the section of Department of Defense responsible for developing a layered defense against ballistic missiles.To the unpleasant surprise of the US, Canada announced in February 2005 that it will not participate in the U.Using complementary interceptors, land-,  sea-, air- and space-based sensors, and battle  management command and control systems, the  planned missile defense system will be able  to engage all classes and ranges of ballistic  missile threats.ballistic missile defense system, see National Missile Defense in Canada