Slitherine

Been meaning to ask that when I setup a multiplayer challenge, but could not find it in the online help

This is from the online "help":

Double moves is an optional rule selected on starting a new battle.
When double moves are enabled a battle groups movement allowance is increase by up to three or double its current movement allowance. Which ever is lower.
To be able to double move a battle group must start and end its whole move at least five hexes away from all enemy battle groups.
Hexes that can only be reached by a double move are highlighted slightly differently to normal movement hexes.
e.g. A light horse battle groups movement allowance increases by three to eight. A heavy foot battle group movement allowance doubles from two to four.

I've found the best way to find out stuff in the "help" files is to go to the index and look for the specific item youo need rather than wandering through the hot links.

Deeter

It's to simulate a unit that isn't in combat, or in the near vicinity of enemy (so not having to be wary and careful), doing a double-time forced march to cover greater distance to either engage the enemy quicker, do some form of flanking move or to reinforce a different part of the army.

That too.

Deeter

I think... but not certain, that you must be within a "commander's radius" prior to starting the move.

Also true. You can also move a leader to out of command units and they will be able to double move.

Deeter