Those gray things LOOK like gas turbines, but they aren't. It would be one heck of a crive shaft to connect them from up there to the reduction gears in the engine rooms for propulsion.
FYI: Gas turbines make a heck of a difference. I was stationed on 2 different 378-foot Coast Guard cutters in the early-mid 1970's. Under normal conditions, they used two diesel-electric setups for propulsion and could do 22 knots. They also have two gas turbines installed for when the ship has to get somewhere in a hurry. With the turbines on the line, they could easily do 32 knots or more. However, the fuel consumption rate was drastically increased when running the turbines. On diesel, the ship's range was 12,500 miles. With the turbines on the line, the range was reduced to 2,500. Yep, the ships can really haul cheeks, but not economically.