Mk20 mod1 Electro Optic Sensor System (EOSS)
The War Zone provides a discussion of a frequently overlooked bit of hardware that the National Security Cutters share with Cruisers and Burke class destroyers.
I did a short post about this system back in 2017.
What is it good for?
“The primary purpose of the system is to provide highly accurate targeting information to the ship’s gun weapon system. In many instances, the ship’s radar may make an initial detection of a potential threat, and the Mk20 is then cued to visually confirm the target, and provide precise range and position for gun engagement. The goal is first shot hit accuracy. Of course, sailors are quite creative and immediately recognize the Mk20’s excellent performance as a situational awareness and navigation aid. We have heard of crews using the Mk20 to visually investigate suspicious vessels, and help navigate through congested waters. The operators find the thermal imaging capability and resolution particularly useful in nighttime operations.”
Chuck Hill's CG Blog 
When in EMCON no radar emissions are permitted, as are emissions in the RF (and other) part(s) of the EM spectrum based upon level of employment. However, passive tracking systems have no restrictions.
The U.S. Navy now has systems coming online that detect/track targets based upon IR/motion, and other passive metrics. The Shipboard Panoramic Electro-Optic-Infrared (SPEIR) system is a case in point. The system can detect and track IR targets 360⁰, and provide target queuing. L3 Harris also has SensorXP (a part of the SPEIR system). For the first time the U.S. Navy now has a passive detection/tracking/designation & fire control system for Surface Combatants. We should see an article on this/these system(s).
This system can support guided rocket systems very easily right down to laser target designation.
We have been a long time in waiting for SPEIR now. Chuck first mentioned it on here in 2022. Indication it won’t be on a ship until 2027. Everything takes too long.
AMEN! AND . . . everyone needs one. One should be on the CSEDS mast already!