Also, bear in mind that any mast stuck up out of the water runs the risk of getting sniffed by radar. Any ship or merchant in the area that picks it up could pass the information on to the Iranians, who might just be able to get one of their Kilos working long enough to deploy it, or send over a little ASW ship to make the Newport News's life a bit more difficult.
So the NN was probably relying more on sonar than visual, and like I said, sonar condictions in Med-like waters can be very misleading.
Either that, or the US Navy is still fighting World War 2
