Cross Sector Reinforcements

Retreat may not work in the simulator because there is no sector for the ships to retreat into.

You cannot bring reinforcements in during the middle of a battle. In simultaneous movement games (eg: PBW), if you get the fleets to arrive in the target sector on the same day, they may participate in one big battle.

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Yeah I'm pretty sure it doesn't retreat properly in a simulation because there is nowhere to retreat to.

I consider the whole month when planning battles. If all you do is head for the enemy and fight it's not any different to running into them, but if you plan movements from different directions then you have the advanatage. Try and look at the sector where your enemy is, see where his ships are located. For example, and I don't think I've ever managed it but I keep it in mind, you could move one group of ships in from say the east and his warships, which might be on the east side of the sector will attack them. Meanwhile his support ships on the other side of the map will be easy prey to a smaller force that appears at the same time. I sometimes get tired of planning elaborately and setting up units by hand just to make sure I'll have the advantage, but I've come to realise that I win battles because I am prepared to plan and set up units by hand.

Keep in mind that the month is 30 days. Figure out which days ships will move depending on their movement rate, and if two fleets have the same movement then they can enter an enemy sector on the same day, but from different directions.