Final answer:
The J-series message mentioned is true; it's used for communicating mission assignments, target designations, and target information to non C2 platforms within military operations.
Step-by-step explanation:
The J-series messages you are referring to are part of a military communication protocol used to convey mission information, targeting data, and orders to various units. In particular, the message you mentioned is indeed used by Joint (JU) commanders or units to assign mission objectives, designate targets for action, and relay pertinent target information to platforms that are not part of the command and control (C2) nodes.
Thus, the statement is true. These messages are crucial for ensuring coordinated action in military operations, providing non-C2 platforms with the necessary information to execute their part of the overall mission.