If it is indeed GPS spoofing it must be happening to commercial vessels right? Doesn't the US military use a different, more accurate/secure version of GPS? It seems more likely the less secure AIS protocol is somehow being manipulated.
However, these collisions could be caused by spoofing the general maritime traffic so the US ships are on the 'correct' course and everyone else is offset.
These collisions could not be caused by anything but massive human failure, because while the military may exploit networked electronic conveniences to track expected civilian traffic positions, that's not supposed to be the only system they have.
And they'd be useless as warships if that was their only way of detecting larger ships than their own size short of bumping into them.
There are also military specific parts of GPS that civilian receivers can't access. I don't know if military receivers are ignoring civilian signals, though.
For all intents it's a different system, the packets are encrypted, the right receiver hardware gives you vastly superior accuracy. There's civilian hardware which can use the packets without decrypting them for better accuracy, there's some patents on doing this amusingly.