A submarine can submerge and avoid attack. They can also surface for a period of time to run their diesel engines in order to recharge their batteries and get the air needed to stay above water.
Type 21 U-boat (or type xxi) is a submarine that the German navy used during World War II. They were a significant improvement on earlier German submarines.
They were able, unlike their predecessors, to submerge longer and more frequently. They were able to do this by using a new technology called the Schnorchel.
This technology was a major breakthrough in submarine construction. It marked a significant change in the design and construction of submarines. The new Schnorchel engine was small and compact. It could be mounted inside a U-boat's hull to allow it to submerge for longer periods than other designs.
This technology was a breakthrough and allowed the Germans construct larger, more powerful submarines capable of enduring more attacks. This enabled them be able keep their crews afloat and to fight longer, which ultimately helped them win war.
But, the Schnorchel's greatest advantage was that they could reload their torpedoes whilst still submerged. This was a major win for the Germans. This allowed them to be more active in the water, hunting for enemy vessels and reducing the need to refill their torpedoes.
Type XXI (a German U-boat) was built in Germany as the first. It was intended to become the German new submarine and help them win World War II. It was also a failure and may have contributed to the Third Reich's defeat.
A few years prior to the XXI, the Germans were working on a new design for submarines that would change the game. However, it was a gamble and they weren’t prepared to take that risk. They were not sure the new boat would work well, and they didn’t want to spend a lot on something that might fail.
They were able, however, to produce a prototype in Apri 1944. That gave them hope that production could begin sooner. This new design was based on Walter gas turbines which were used in the original designs. It was also doubled by new Deutz SAA SM517 supercharged, 8-cylinder diesel engines. Combining these engines with the streamlining in the hull gave rise to seventeen knots.
The gamble was a massive one for the Germans and Donitz had to make a difficult decision between giving up submarine warfare completely or gambling on the new design. He was aware that the war would be over if he didn’t have the new boat. He also knew that the new boat could do more than simply reload torpedoes, which was a major plus.