As modern militaries are evolving their military command and control systems, it has become an important issue to test tactical data systems (TDSs) using Variable Message Format (VMF) messages because VMF is a common means for exchanging tactical data between combat units at various organizational levels. VMF has presence/recurrence fields allowing the user to send a minimal length message without losing information, but it causes the length of a message to vary, thereby making message validation non-trivial. Furthermore, VMF includes semantic message rules that help define precisely the interrelationship between the values of different fields, but it makes validating such relationships difficult. This paper presents our method and evaluation results for overcoming these challenges by applying a systematic test generation method for VMF Tactical Data Link messages. Our method consists of the principles and the derivation of the test requirements, as well as a procedure for test generation based on them. We applied the method in developing a VMF test tool and used the tool to test the various versions of a VMF message parser. We confirmed our method was effective in reducing the complexity of testing that arises due to the message length variability and semantic rules.