Light does not travel well underwater, so visual observation of other ships is almost impossible. Sound travels well and far. The science of listening for other ships has advanced a lot over the last 50 years.

If the submarine had a window, and if you could see through the water, you might see a view something like this photograph. There are special circumstances that will allow enough vision to make a photograph like this one.

When the submarine is surfaced or at periscope depth it is again possible to visually observe the surrounding area. The old tested tried and true periscope is still a usable device to passively gather data on the area surrounding the submarine. It can still be used to passively take data in preparation for an attack on a surface target or to spy on some other vessel or object. There have been improvements in the device, such as high resolution Television attachments, but it remains a periscope.

The classic weapon of a submarine is its torpedoes. Torpedoes have changed very much over the last 50 years. In old movies you saw the submarine being pointed directly at the target and the torpedoes ran in a strait line from the submarine to the target. Today's weapons are fired without concern about the relative bearing to a target and they are able to guide themselves to a target. Calculations are accomplished using powerful computers. The modern torpedo can search and locate a target and attack it using its own sensors and intelligence. In military talk they are Fire And Forget units.