They may have suffered mechanical breakdown on one and drifted into territorial waters surrounding an Iranian island in the middle of the Gulf
http://www.nytimes.com/2016/01/13/wo...=tw-share&_r=0
"It was unclear how contact with the boats had been lost, and Navy officials in Washington said they were trying to determine what had happened. One official said the two vessels had failed to make a scheduled rendezvous with a larger ship to refuel."
I have difficulty understanding why even if one failed there was no tow and they would allow themselves to drift. Unless they both ran out ?? Smells fishy.