How would you control them? Telepathically... ??
The same way guard dogs are controlled, through training. Dolphins perform several missions, but are most commonly used to locate mines. They wear a small “pinger” that acts as the sounding device for a remotely operated sonar. They are also used to retrieve objects using devices they carry in their mouths. In an antipersonnel setting, they will swim around until they find a target, return to a buoy or boat and get the okie-dokie and the weapon. I don’t know if that system is currently deployed or operational, but it has been developed. Sealions perform many of the same duties.