USNI:
The Aegis ballistic missile defense (BMD) program, which is carried out by the Missile Defense Agency (MDA) and the Navy, gives Navy Aegis cruisers and destroyers a capability for conducting BMD operations. Under the FY2019 budget submission, the number of BMD-capable Aegis ships is scheduled to be 41 at the end of FY2019 and 57 at the end of FY2023.
Two Japan-homeported Navy BMD-capable Aegis destroyers included in the above figures—the Fitzgerald (DDG-62) and the John S McCain (DDG-56)—were seriously damaged in collisions with merchant ships in waters off the coasts of Japan and Singapore in June 2017 and August 2017, respectively, and are currently being repaired.
The temporary loss of these two BMD- capable ships reinforced, at the margin, concerns among some observers about required numbers of BMD-capable Aegis ships versus available numbers of BMD-capable Aegis ships, particularly for performing BMD operations in the Western Pacific.