I DID IT !!!!!!!! I FOUND THEM !!!
Below are spoilers to beat the scenario.....
You need to make a shipyard..... Then create a the first type of ship. I can't remember the name. On it's description it says it Detects. Once it is created take it to the middle of the map between the towers.... A HUGE underwater city is then revealed. Elimitate the underwater Tower Room Building and the mission is over.
Note to us dummies.... If we bothered to read the objective...... it told us the whole time that Detecter Ships were needed !!!!