Weapons and sensors have made great advances

 

 Deck guns have been omitted and in some cases anti-ship missiles have been used. Torpedoes are capable of speeds of over 50 knots and navigate to their target acoustically using integrated sonar or are controlled by electronic commands transmitted through thread-like wires that follow behind the fast-moving projectile. In addition, many submarines are equipped with cruise missiles or anti-ship missiles for attacking targets on land or at the surface. Submarine sonar for detecting surface ships and other submarines has been significantly improved and the familiar periscope is replaced in modern submarines by the so-called photonic or optronic mast. These are sensor systems that extend to the surface like a periscope from a submarine's sails. Unlike them, however, they transmit optical, infrared, and radio information electronically to the control room without requiring hardware that penetrates the submarine's hull. The masts are controlled in the control room with simple joysticks, and data is available on screens located throughout the submarine.

 

Maximum diving speed has only been increased slightly (over 20 knots) compared to the German Type XXI, and endurance at top speed is no greater than at the end of World War II. Improvements in the design of conventional lead-acid batteries have somewhat improved low-speed endurance. For example, many modern submarines can remain submerged for a week to 10 days (at about 3 knots). This is an important improvement because over such a long period of time, sea conditions could easily develop that would cause the submarine to escape or scatter submarine hunters on the surface. But an even bigger improvement has come with the development of "air independent propulsion" (AIP) using fuel cells. Some AIP-capable submarines are said to be equipped with fuel cells that use stored hydrogen and oxygen to generate electricity, allowing them to operate at slow speeds underwater for up to a month.