In the prototype, there were two antennas for track while scan operation: slotted waveguide antenna for searching and cassegrain antenna for tracking.
Both antennas were covered with a radome.
Also outside of the radome, an electro-optical tracker was installed.
As a fire-control computer, digital electronic computer was installed instead of an electromechanical analog computer of the FCS-1.

Mass production versions were put into service with destroyers and destroyer escorts built under the FY1977 program.
On the Hatsuyuki-class destroyer, a combination of one FCS-2-12 and one FCS-2-21 was adopted at the beginning.
FCS-2-12 is very similar to the prototype, but adds a missile guidance function.
FCS-2-21A is a simplified version specialized in gun fire-control, adding an electro-optical tracker on the left side of tracking radar antenna and omitting the search radar antenna.
And a FCS-2-21B was installed on the destroyer escort Ishikari, which introduced a Passive electronically scanned array antenna instead of a cassegrain antenna and was capable of searching.
Then many minor change models were developed.

In the second-generation DDs, two FCS-2-31 are installed, not a combination of two heterogeneous models.
In this model, a dish similar to 2-21A controls both a medium-caliber gun and Sea Sparrow missiles.
In the prototype, there were two antennas for track while scan operation: slotted waveguide antenna for searching and cassegrain antenna for tracking. Both antennas were covered with a radome. Also outside of the radome, an electro-optical tracker was installed. As a fire-control computer, digital electronic computer was installed instead of an electromechanical analog computer of the FCS-1. 
Mass production versions were put into service with destroyers and destroyer escorts built under the FY1977 program. On the Hatsuyuki-class destroyer, a combination of one FCS-2-12 and one FCS-2-21 was adopted at the beginning. FCS-2-12 is very similar to the prototype, but adds a missile guidance function. FCS-2-21A is a simplified version specialized in gun fire-control, adding an electro-optical tracker on the left side of tracking radar antenna and omitting the search radar antenna. And a FCS-2-21B was installed on the destroyer escort Ishikari, which introduced a Passive electronically scanned array antenna instead of a cassegrain antenna and was capable of searching. Then many minor change models were developed.
In the second-generation DDs, two FCS-2-31 are installed, not a combination of two heterogeneous models. In this model, a dish similar to 2-21A controls both a medium-caliber gun and Sea Sparrow missiles.
FCS-2