Here you are:
I've been working for some time now on a squadron/fleet-level TRAVELLER wargame that is intended to put the player in the role of the Sector Admiral defending against invasion; sort of a new version of Fifth Frontier War, if you will. I think I have most of it worked out, but I want to add more "crunchy tactical goodness" (as Ken Burnside calls it) to the battles that take place in systems that the player is not personally at. I'd like more than "Add up the fleet strengths, roll on the Results Table, modify the roll according to the Admiral's skill" but I don't want it to take much more time than that to resolve such battles. I think I've worked out the intersecting decision trees of both the Invading admiral and the Native admiral, and reduced the intersections to a table, but I'd like others to check my logic and see if it's reasonably valid.
First, some assumptions. Both fleets have similar weapon ranges and accelerations. The Intruder fleet must exit Jump outside weapons range of the target, so both sides can see what's coming. While it is impossible to completely hide maneuvering ships, deception about numbers and types of ships is possible. This is for resolving battles with invading fleets, not for dealing with raiding forces.
I see the Intruder having two initial choices: go for the planet, or go for the defending fleet. Inside those choices I see two more for each option: if going for the planet, you can either go quickly and overrun the world, or you can approach cautiously. Overrunning is the optimal choice if you have plenty of force, while caution is advised if you're not sure. If the enemy fleet is the objective, again I see two main choices; lure the enemy into battle by appearing weaker than you really are, or trap him into battle by dividing your forces so he can't avoid a fight with at least some of your fleet.
Explaining those options: I put things as a choice between the enemy world and the enemy fleet because if the Intruder has enough strength to go for both at the same time, how much fighting can there be anyway? Besides, you know where the planet will be, so you can always deal with it later. The reason to have the planet as a possible objective is that you might need the planet quickly, or the enemy fleet might stand to defend it so you could get a "two-for-one" deal. "Lure" is the option to pick when you think the enemy fleet also wants a battle. You certainly wouldn't divide your fleet against a willing enemy, and it never hurts to make your enemy a little overoptimistic.
For the Native (defending) fleet, I also see two main options, each with two sub-choices. The defending fleet can run for it, in which case it can either split up or run as a single force. If the defender splits up, they're not looking for a fight at all; if running together they still aren't looking for a fight, but they will fight to get clear. The other main choice the defender can make is to stay and defend the planet. I see two options inside that choice: stay at the planet, so planetary weapons (deep meson gun sites) can help, or fight away from the planet so it can't be bombed.
When you put the Intruder choices along the top of a grid, and the Native choices along the side of that grid, you end up with a table that I thinks looks like this:
Choices | Overrun planet | Cautiously approach planet | Lure defenders into battle | Trap defenders into battle |
Split up and run for it | No fleet battle, proceed to planetary bomb/invasion, Native may Jump | No fleet battle, proceed to planetary bomb/invasion, Native may Jump | No fleet battle, proceed to planetary bomb/invasion, Native may Jump | Random Native losses, proceed to planetary bomb/invasion, surviving Native may Jump |
Stay together and run for it | No fleet battle, proceed to planetary bomb/invasion, Native may Jump | No fleet battle, proceed to planetary bomb/invasion, Native may Jump | Passing battle if the Native chooses, surviving Native may Jump | Passing battle if the Intruder chooses, surviving Native may Jump |
Defend the planet at the planet | Passing battle at planet | Meeting battle at planet if the Intruder chooses | Meeting battle at planet if the Intruder chooses | Meeting battle at planet if the Intruder chooses |
Defend the planet away from the planet | Passing battle away from planet, then passing battle with planet, surviving Native may Jump | Meeting battle away from planet if the Intruder chooses, surviving Native may Jump | Meeting battle away from planet if the Native chooses, surviving Native may Jump if Native chose battle | Meeting battle away from planet if the Intruder chooses, surviving Native may Jump |
If the Natives split up and run for it, the only naval fighting will be between isolated Native ships and the trapping Intruder forces. That will go badly for those Native ships that get caught, but most should get away.
If the Natives stay together as they run, and the Intruders go for the planet, the Natives get clean away. If the Natives run as a unit and the Intruder was luring them into a battle, the battle will happen if the Native chooses battle (if he falls for the lure). If the Native runs as a unit and the Intruder set a trap, then the battle happens if the Intruder chooses (if he thinks his divided fleet can still muster enough strength). Both of these battles will most likely be what I call “passing battles.” I think passing battles will occur when one or both sides want a short, sharp engagement. The fleets will pass through/by each other at relatively high opposing vectors, such as when one fleet is really just trying to get to the Jump limit. Passing battles would open with one missile barrage as the fleets approach and then a burst of energy fire and missiles as the two forces intermingle. Once the forces pass there’s no more shooting as they would be out of energy range, and running away from missiles.
If the Natives stay with the planet they are giving the initiative to the Intruder who can choose or refuse battle. Such battles would be what I term “meeting battles,” which are like the battle you get in High Guard. The fleets are closing at a low relative velocity, and either side can maneuver to change the range. I see these engagements as being slow, attritional missile engagements.
Of course, if the Intruder committed to overrunning the planet, there will be a passing battle at the world. If the Intruder committed to overrunning the planet, and the Native chose to defend the world away from the planet, there will be two passing battles: one with the Native fleet, and one with the planet as the remaining Intruders overrun the world.
Otherwise, if the Native chose to defend away from the planet we have several possibilities. If the Intruder approached the planet cautiously, a meeting battle away from the planet will happen if the Intruder wants it. Since the Intruder’s vector will be low (cautious approach) he can quickly reverse and either slow the Native’s overtake (if the Intruder wants battle) or avoid contact entirely. I see the same being true if the Intruder split up his forces to trap the Native. The Intruder doesn’t have to fight unless he wants to keep the Native forces from escaping into Jump. The Intruder can always chose to let the Native go if the odds don’t look right.
Now if the Native is seeking battle away from the planet, and the Intruder is trying to lure the Native into battle, a battle will happen if the Native chooses. Either the Native thinks he can win or he has fallen for the lure. If the Native refuses battle, the Intruder cannot force it on him (the Intruder was trying to lure the Native out, after all) but the Native cannot Jump away since they turned away from the Intruder.