Final answer:
The Link 16 message used for free text messaging is the J2.2 message, a part of a tactical data exchange network used for adaptable communication in military operations.
Step-by-step explanation:
The message used for free text messaging in the Link 16 tactical data link communication network is known as the J2.2 message. Link 16 is a military tactical data exchange network used by various NATO and allied forces for communication and information sharing. The J2.2 message format allows for the transmission of free-form text between units, facilitating a versatile communication method beyond predefined message formats. This capability is especially useful in complex military operations where quick and adaptable communication channels are necessary.