True, but having hired several Navy electronics techs when I was in the wireless telecom biz, I have full confidence that the techs on those ships could cobble something together that would do DF. A yaggi hooked to a spectrum analyzer would be all they needed for a crude direction finder. The guys I hired were some pretty smart fellas with excellent troubleshooting skills, even on devices they'd never seen before. Considering they had no real formal engineering training, their level of knowledge of complex circuitry was quite impressive. I'm told the Navy teaches their techs a lot more theory and less about how to just fix a particular box, compared to the other branches of the military. This is especially true for the sub guys. After all, there ain't no service calls out in the middle of the ocean....
... as there would be no reason for that.
Seems like there is a pretty good reason to have the capability now.....
There is not doubt they could do it, but to counter threats made by a vessel in line of sight would not win them any prizes for brilliant thinking or utility.
The chances of any vessel warning the US Navy that is it is going to attack them is only credible to gullible.