system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do modern military generals use ancient military tactics/strategy's?

I hear this every so often when I watch historical documentaries, for example they go on about a certain tactic or strategy that Alexander the Great used in a battle and then they say that a modern general used the same tactic in a modern battle, but how can that be possible with all the changes to military hardware, the use of tanks and other things?

Just wanting to know how it can be transferable aside from just taking basic movement tactics or something else from basic.
gpt
On the level of military *hardware*, you're right. A lot has changed in the last few thousand years.

But the *goals* of military conflict are basically unchanged: do enough damage to the other guy that he can no longer prevent you from carrying out your operational objectives while keeping one's own casualties to an acceptable minimum. 

With that in mind, certain patterns emerge, patterns that can be applied *across* history, even if the specific way they are *implemented* has changed rather drastically over time. Examples, many of which overlap:

* If at all possible, fight at a place of your choosing, not a place of your enemy's choosing. 
* Don't attack a fortified position if there's any way of avoiding it. 
* The mobile force has the operational advantage over the force that is fixed in place.
* Attack when your enemy least expects it, not when he would prefer it.
* Attack from the direction your enemy least expects it (one of the things mobility lets you do), not from the direction he has anticipated.
* Attack where your enemy is weakest, not where he is strongest.
* Attack in ways your enemy is least prepared to defend against, not in ways he has anticipated.
* It doesn't matter how many more troops one side has if he can't bring them all to bear at the same place and same time.

So yes, *particular* tactics, e.g., the massed heavy cavalry charge, the spear-armed phalanx, the massed infantry charge, broadside-style naval tactics, have certainly gone by the board as military hardware has evolved. And even where *categories* of tactic/formation have survived, the *specifics* will change with hardware (e.g., there's a reason tank units are called "armored cavalry"; many of the principles are the same, even if range is measured in tank fuel instead of horse feed, etc.). But a commander focused on pulling off specific tactics obviously suggested by his hardware has, in the long run, already lost. The successful commander will remain focused on *accomplishing his objectives*, and will seek to use whatever hardware is at his disposal in bringing that off as efficiently as possible, guided by principles like those listed above.