In 2000, the Japan Defense Agency Maritime Staff Office included another two Aegis ships in its five-year budget on top of the four Kongō-class destroyers originally ordered.

The Atago class is fundamentally an improved and scaled-up version of Kongō-class destroyers. The class features large accommodation and the ships are capable of flexible operation. One of the most obvious changes is an additional hangar to carry one SH-60K helicopter. In comparison to the Kongō class/Arleigh Burke class (Flight I) which only had helicopter platforms (but no support equipment), these ships have better helicopter handling facilities. To enhance the Atago class' function as command centers, the bridge is two decks higher than aboard a Arleigh Burke class Flight IIA, making their full load displacement over 10,000 tons—the first time for a JMSDF surface combat vessel. The gun caliber has extended from the 54 caliber of the Kongō class to the 62 caliber with strengthened powder charge capable 38 km firing range. As with other Japanese ships being refit, the American-made Harpoon missiles (such as in the initial configuration of the Kongō class) have been replaced with the Japanese-made Type 90 (SSM-1B) surface-to-surface guided missiles.

Japan has also purchased a manufacturing license for these weapons for use on their Kongō-class Aegis destroyers. Japan Steel Works will manufacture, assemble and test the weapons.

The fire-control system for the Atago class is the Aegis Weapon System Baseline 7 phase 1, which will combine American- and Japanese-manufactured systems to make up the complete Aegis system. The Aegis Weapon System baseline 7 has improved tracking accuracy for vertical targets, and an acquisition capability for small low-altitude targets compared with the Aegis Weapon System baseline 4 and 5, used in Kongō class. The Atagos also use a new stealthier plain-structure mast, which was originally designed in Japan, rather than familiar lattice type mast. A new modified smokestack and other improvements were also introduced to make the Atagos stealthier. (Wikipedia)

DD-177 AtagoDD-178 Ashigara