How long does it take to communicate with “trained” mounts?

Question

In the PHB (p.198) mounts are either controlled or independent.

Controlled mounts have only three actions, move, disengage, or dash. Combat is not an option.

Uncontrolled mounts can take whatever action they desire independent of their rider.

It seems somewhat clear how intelligent mounts might act. For example, a dragon could be told to attack a particular foe and it just might obey your commands.

But what about trained mounts like warhorses with limited intelligence? In actual historical battles, war horses could “attack” opponents using the 5e equivalents of the “Shove” action or “Shove Aside” action or “Trample” as in previous editions of D&D. (Trample seems to apparently no longer exists as we are unable to find any references across PHB, MM, or DMG.)

In 5e if you take “control” of a mount, it cannot take those Attack actions.

Given that, what 5e guidance is there for issuing commands to “uncontrolled” but trained mounts? Can one use the reins to direct a warhorse to trample an opponent or give more complex non-verbal commands like turn, charge and attack?

Most importantly, assuming these commands can be issued, what guidance does RAW give regarding how long those commands would take? Would these be considered actions allowable during one’s turn or would they take a Full Action or Bonus Action?

Answer 1

Commands are free

Commanding something appears frequently in the PHB, and in each case, it uses wording something like this:

On your turn, you can verbally command the beast where to move (no action required by you).

This wording appears in the the various Conjure [creature] spells and the Ranger Beastmaster's Ranger's Companion feature, and probably other places I missed. Assuming that you have a beast that can follow your verbal commands, giving such commands costs no actions.

This conclusion is further supported by this section in the PHB (190):

You can communicate however you are able, through brief utterances and gestures, as you take your turn. You can also interact with one object or feature of the environment for free...

Thus, if the mount is trained to do so, you can use the reins of your horse to direct it to attack, since it would be your free object interaction.

Of course, the DM can decide that what you're attempting to do is too complicated and requires an action, as well:

The DM might require you to use an action for any of these activities when it needs special care or when it presents an unusual obstacle.

Answer 2

If you are riding a trained mount of low intelligence and giving it commands, it is, by definition, a controlled mount, and therefore cannot attack. In order for a low intelligence creature to be uncontrolled, you would need to not give it commands.

Uncontrolled mounts are NPCs fully controlled by the DM that you just happen to share a space with. You interact with them as such (however your DM wants).