Warriors Adapt and Overcome in Chinese / Japanese...

This literally translates as: Troops/soldiers/warriors have no fixed [battlefield] strategy [just as] water has no constant shape [but adapts itself to whatever container it is in].

Figuratively, this means: One should seek to find whatever strategy or method is best suited to resolving each individual problem.

This proverb is about as close as you can get to the military idea of “adapt improvise overcome.” 兵無常勢水無常形 is the best way to express that idea in both an ancient way, and a very natural way in Chinese.