The pentagon said on a week ago that the USNS Impeccable that showed the habit increasingly aggressive and this matter became severe last Sunday.  

The Pentagon issued their statement about the USNS Impeccable, the United State surveillance ship, for the development matter that happened a few days ago. They said that:  

[Five Chinese ships had] shadowed and aggressively maneuvered in dangerously close proximity to USNS Impeccable, in an apparent coordinated effort to harass the U.S. ocean surveillance ship while it was conducting routine operations in international waters.

The five Chinese ships shadowed and has maneuvered the aggressive and dangerous acts in a near distance from USNS Impeccable and that act estimated would interfered the USNS while that surveillance ship did the routine operation in the international ocean.