To see a tank filled with water in your dream signifies prosperity and satisfaction with the current state of your life. You have complete control over your emotions. If there is a faceless human/fish-like creature inside the tank, then it implies that you are keeping an aspect of your emotions bottled up. You are afraid of confronting your own feelings.
To see a military tank in your dream represents the need to defend yourself and stand up for your beliefs, even if it means being confrontational or violent. You are not letting anything or anybody stand in your way toward your goals. Alternatively, the tank symbolises a threat.
Dreaming about a tank car on a train indicates that your feelings are predictable. Alternatively, seeing tank cars in your dream mean that you tend to not let your emotions get in the way of your decisions. You know how to stay objective.