Tactics

The opponent's headquarters is located in the 2nd from bottom row (between 2 buildings).

So that it lies within a little more than 11 spaces from your army.
diagram2

Yet, according to the rules of the game, pieces may advance at most 3 spaces at a time.
diagram3

It therefore takes time to move into the opponent's headquarters.
How, then does one go about capturing it?

1. Tactics to capture headquarters

First of all, remember two simple rules.  They are the same as in Chess.

1. The opponent's headquarters can be captured as long as even one piece reaches it.
   (In the game of Chess, you must take the King).
   diagram3
2. You can only take one of your opponent's pieces in on e round.
   (In Chess also, you can take only one piece in one round).
   *However, the following rule is different from Chess.

3. Each piece can move a maximum of 3 spaces
   

In Chess, movement differs depending on the piece.
In Strat-X, movement is restricted to horizontal and vertical, and is restricted to a maximum of 3 squares. 
diagram2

Why does this rule exist?  This is because if pieces could move many squares at a time, the game would end too quickly. 

So how do you capture headquarters?

Remember that "the maximum a piece can move is 3 squares". 
From this we see that "if we are within 3 squares of the opponent's headquarters, it'll result in capture".
However, even if a piece moves within 3 squares of the headquarters, what happens if it is only one?
Then, it will no doubt be taken down by a nearby piece. 
Here, remember that "in one round, only one piece can be attacked".
So that as long as there are 2 of your pieces within 3 squares of the headquarters, you are assured a capture.

Even if one of your pieces is taken, the other remains alive. 
And this one piece can take the headquarters.

Of course, moving two of your pieces within 3 squares of your opponent's headquarters is far from easy.
Movement is slow (up to 3 squares per round) and your pieces will be attacked before they reach there.
What then can one do?

Let's first start with a simple calculation.
If there is a skirmish, each player attacks the other.
The side with more pieces comes out of it alive.
If, for example, there are 2 of your opponent's pieces and 3 of yours, and there is a skirmish, and both sides suffer 2 losses,
diagram6 then one of your pieces remains.
diagram7
And this one piece can move on to capture headquarters. 
diagram8

"Strength in numbers" is a basic principal in battle.
So for example, if there are 3 pieces defending your opponent's headquarters, you should attack with 4 pieces.
If there are 4 defending, attack with 5.
So you should advance with as many men as possible.
Don't advance with a small company, for they will all be assailed.
The basic strategy is, in the opening of the game, "to advance slowly with as many men as possible, concentrating your forces".

In the game of Chess, any piece may take any piece.
However, in Strat-X, there are certain pieces that certain types of pieces cannot attack.
Of course two pieces of the same type, like two tanks, can attack each other.
And tanks can attack artillery.  But "infantry cannot attack tanks" because their bullets cannot penetrate the armor of tanks.
To see which pieces can be attacked by what, refer to the table.
diagram9 In Strat-X there are only 3 types of pieces.
And the three pieces have a stone/scissors/paper relationship.

What strategy is born from this?  For example, let's say a group of tanks advances.
But the opponent has artillery.
Your tanks cannot attack the artillery, so your company is all blown away.
diagram10 What if your company is made u of only infantry? 
Then if your opponent comes out with a tank, then your whole company will be obliterated.
diagram11
In other words, one cannot hope to win by advancing only one type of piece.
As such, there ought to be different types of pieces within one battalion.
diagram12

Therefore, when the opponent's infantry advances, send out your tanks.
When their artillery advances, stop them with your infantry.
A basic battle formation consists of 3 or more infantry, 2 or more tanks, and 1 or more artillery, advancing together as a group.
diagram13
A piece on its own does not constitute military strength, so to keep pieces together is important.
Pieces demonstrate their war potential only as a group.

On the board there are obstacles such as mountains, buildings and trees.
It is not only that pieces cannot move into them.
Your pieces can also hide behind them from attack.
diagram14
Mountains, where only tanks can pass, are especially useful.  For example, say a tank hides behind a mountain.
diagram14
This tank can come through the mountain, attack the opponent,
diagram15
diagram16
and then once again hide behind the mountain.
diagram17

Lakes are obstacles through which pieces cannot pass, but do not act as barriers as they have no height.