The German Kreigsmarine of World War II were credited with the creation of the first Submarine Vessel capable of complete submersible (underwater) operations. The established operations of Submarines during World War 1 and II, gave Submarines the abilities to stay submerged for very short periods of times. These periods of operation were used for surveillance and actual deployment of weapons. Diesel powered, they used electric power to maintain power (electricity). Submarines needed to surface to replenish their air compressors for breathable air.
To establish a truly “submersible” Vessel, Germany began to develop The “21”-Class of Submarines around 1943. These Vessels (the first completely "electric" powered) were designed to remain totally submerged for days at a time, requiring only to surface to a “safe depth” to extend tubing (snorkel) – for fresh air replenishment. The “21”-Class was considered totally electric and used 6- Diesel 6-cylinder Engines. In addition, twin “Silent” rigged Engines were installed which made typical detection underwater by Sonar virtually impossible with the technology of The Era.
The “21”-Class had great speed for a submersible, rated at 25-mph while underwater. They could range for 17,000-miles, making them unique to submarine warfare. They had a maximum depth range of 787-feet. The “21”-Class of Submarine was 250-feet long with a 30-foot beam. They typically crewed 60-men. Armament for The “21” was (6) 21-inch Torpedoes and (23) Mines – which could be deployed and armed underwater. They also had (4) 2cm Machine Guns for surface defense.
The Class of Submarines (of which 118 were finally constructed), had design flaws that were hard to correct due to a shortage of materials and proper training. As a result only 4 “21”-Class were actually deployed in combat. The War ended with these Ships never being used to sink Allied Shipping. Had The “21”-Class been fully deployed – it is speculated, the tide in Naval Warfare in The Atlantic would have changed in favor of Germany fairly quickly. However, as a result of capture by Allied Forces. The “21”-Class would advance Submarine design and warfare.