In order to defend against a possible ballistic missile attack from North Korea, Japan has decided to deploy Patriot Advanced Capability 3 (PAC-3) anti-missile defense units at several strategic locations.
Japan has already deployed AEGIS destroyers that are armed with the RIM-171 Standard Missile 3 (SM-3). The SM-3 is launched from the Mark 41 Vertical Launch System.
The Japanese Navy has 4 Kongo class destroyers and 2 Atago class destroyers that are equipped with the AEGIS system. The Kongo class is based on the Arleigh Burke class destroyer. The Atago classis a further improved version of the Kongo class.
Due to questionable effectiveness aagainst ballstic missiles of the preceding PAC-2, the PAC-3 was designed from the ground up specifically against ballistic missiles.
It smaller size allows you to fit 4 PAC-3 missiles in the same space of a single PAC-2. However, it's also not suitable against traditional targets such as aircraft for which the PAC-2 is still needed.
The PAC-3 is supposed to complement the SM-3 in providing a layered defense against ballistic missile attack. The SM-3 is responsible for missile intercepts in the mid-course phase. Once this has been breached, the PAC-3 is responsible in the terminal phase.
Both the SM-3 and PAC-3 rely on kinetic energy to destroy incoming missiles using the hit-to-kill technique. The PAC-3 also carries an additional explosive charge to enhance its lethality.
The PAC-3 only supports missile intercepts within the atmosphere after missile reentry or endoatmospheric intercepts. The SM-3 can intercept missiles outside the atmosphere or exoatmospheric intercepts.
One drawback of the PAC-3 is its relative short range of less than 30 km against ballistic missiles. An improved version now under development is the Patriot Advanced Capability 3 Missile Segment Enhancement (PAC-3 MSE).
The PAC-3 MSE addresses some shortcomings of its predecessor with a 50 percent improvement in range. The PAC-3 MSE is also faster and more maneuverable.