Are these aircraft so old they are having structural failures? Could it have been an explosion on board?
The design is really old but I have read that they continued to make them and maybe still are.
Most USMC KC-130s are the newer KC-130J models which started rolling out in the late 1990s and are still in current production. However, one of the Reserve VMGR squadrons (in New York) is waiting its turn for the new bird and still flies the older KC-130T. The plane lost in Mississippi is a KC-130T, but it is way to soon to know what went wrong.
IIRC the C-130 and the old Lockheed Electra turboprop had a lot of commonality in their wing structure. The Electra had a problem with wings falling off.