詳細については以下をご覧ください。

"Options for Japan-U.S. Cooperation in Coping with Gray-Zone Operations over the Senkaku Islands"

https://www.nbr.org/publication/options-for-japan-u-s-cooperation-in-coping-with-gray-zone-operations-over-the-senkaku-islands/

"The Gray Zone in the Definition of Gray-Zone Warfare: Challenges for Japan-U.S. Cooperation"

https://www.nbr.org/publication/the-gray-zone-in-the-definition-of-gray-zone-warfare-challenges-for-japan-u-s-cooperation/