Modified.

This is coolbert:

"The Air Force did not say how the GBU-31/Bs had been modified to enable them to engage moving targets. Standard JDAMs have a GPS-assisted Inertial Navigation System (INS) guidance system that can only be used to point them at specific coordinates."

"The Air Force Is Developing Smart Bombs With 'Torpedo-Like' Ship Killing Capability"

"A recent test explored the use of modified Joint Direct Attack Munition bombs against static and moving targets at sea."

From the Internet web site "The Drive" and the article BY JOSEPH TREVITHICK 

See my previous blog entry:

https://militaryanalysis.blogspot.com/2021/09/quicksink.html

Others are asking the same question as I did. HOW has the basic JDAM system been modified so as to be able to hit a MOVING target? JDAM normally only [?] used against a static target the GPS coordinates of which are well established.

A "mix of options" are available to make the JDAM system more robust?

"Some sort of multi-mode guidance system with a mix of options, such as millimeter-wave radar and imagining infrared seekers, in addition to the JDAM's standard GPS/INS combination, could provide this capability. The Air Force already has at least one weapon, the GBU-53/B StormBreaker, in service now with this kind of seeker system."

Think also from the era of WW2 and the German glide bombs Fritz-X and Henschel 293. Effective against naval targets moving. 

This improved version JDAM weapon it is quite clear to me is aimed [quite literally so] at the Chinese navy. Beware China, your naval assets now in much more precarious position. So is the message!

coolbert.