There are some nuances which can cause misunderstanding (if someday Americans and Russians will fight together).
"Есть!" implies that a soldier has got an order from the commander. It sounds like "Aye aye sir!" or "Aye aye captain!".
"Так точно!" means that a soldier agrees with a commander (or other soldiers), literally it sounds like "Exactly so, sir!" but usually it's translated as "Yes, sir!". "Так точно" doesn't mean that a soldier has got a command, it's just a military version of "Yes" or "I agree".
Throbert McGee,
So, there is the difference between "Есть" and "Так точно", don't mix them up.