I would like to take into consideration with you my thoughts on tactical use of the Doom Cannon.

In the first part I will consider it against a cuotl opponent, ignoring financial drain.
In the second part I will consider it against an Alin opponent, ignoring financial drain.
In part three I will show you problems, advantages, disadvantages, and tips on it's use.

The Doomcannon can be of great use against the Cuotl.
If a player has forted, his defence buildings, such as sentinels and sanctuaries, are able to destroy an invasion on their own.
The Doomcannon can be used twice in an attack - or even 3 times! First, use the demolition shell at the attack point, using a cheap telescope to see where to fire it. Next, begin the engagement at the breach point, and use the shrapnel shell...
- The Cuotl Player can lose a lot of his units, which are more powerful than with the other races - and with reduced numbers you will be able to focus fire on just a few units, no buildings to stop you.
- The Cuotl Player can alternatively move his units. This gives you free ground you dont have to fight over, and the ability to attack his units without any fire being returned. This can be impossible if the engagement has your forces 'tied' together.

So lets see... (= is a sanctuary, - is a sentinel, ^ is a group of units)

BEFORE SHELLING:
=-=-=
^^^^^

AFTER SHELLING (brackets indicate weak or non-existent, _ indicates ground to advance without enemies in the way):
= (=) =
^(^^^)^
OR
= (=) =
_______
^ ^^^ ^

As you can see, both are advantageous to you.
In the first his forces are weak, and/or low in number/non existent!
In the second his units are unable to support his buildings in the repelling of your attack.

The Doomcannon can be useful and/or terrible against the Alin.
The Alin do not really go for forting, usually at least. They are more suited for armies to be moved around, ambushes, envelopements, and the sort.

Instead of big fortifications, you probably have one or two large armies on the field, each in one or two control groups.
This allows an Alin player to immediately move his army away in one direction through selecting two control groups (using shift and normal number controls), or splitting it into two if he lacks time.
The only use of the Doomcannon would seem to be in capturing cities. Of course, the only advantage would be that it isnt as vulnerable to attack the doge using his doges hammer, unless you wanted to destroy a group of buildings.
But, if the player splits his force you could ambush it. I won't tell you what to set up, as I'm still considering that, but basically you could set up 2 ambushes and use poison gas shell on the tougher one. If that makes them flee, fire during the retreat, then join the other ambush. As soon as some sort of military unit returns, reload into transports *oops, gave you a clue* and return to your land.
Of course, unless early in the game the opponent would see your ambush and possibly ambush the ambush.

I'll finish section 2 and 3 after tea.