network54 WAFF member, he is a german btw.
This is kind of a classic issue, and there is a lot of confusion about it.
It is necessary to understand project legacy and concept origins to understand the differences between both ships, and the first thing we must clear about the question is:
None of the ships is overly superior to the other.
U-212 and U-214 are answers to different problems, and therefore they are different.
U-212 is the result of a german requirement for a submarine with a non magnetic hull. This requirement has to do with the average depth of the Baltic Sea (56m). In those circumstances, the most important defence method of a submarine is just to go to the bottom and try to disappear in the sonar. Hence, the need for a non-magnetic steel hull.
Unfortunatelly, non-magnetic steel is also known in the industry as «sweet.steel.» Meaning that it is «softer» than the steel used in the U-214. Thats why a U-214 can go deeper than a U-212, although in the shallow water of the Baltic the U-212 would go un-notices while the U-214 would probably be caught by sonar.
Actually the family legacy of U-212 is not U-209, but the Thyssen project from the 1970s that resulted in the TR-1700 submarine from Argentina. The fastest Diesel-electric submarine in the world. The same basic layout with two decks is also found in the Dolphin class from Israel, although without non-magnetic steel nor AIP.
U-214s legacy is the U-209, although much changed. It is narrower and longer that U-212. It was not thought for the Baltic, but for open deep sea operation. Therefore U-214 will have no bottom of the sea limit, other than the limit imposed by the resistance of its stronger hull.
Both U-214 and U-212 can operate in shallow waters or deep waters, but U-212 has the edge on shallow water, while U-214 has the edge on deep water.
The systems can be changed and installed on either vessels, depending on the requirement of the users.
U-212 has older systems than the U-214 (which is just natural as the projects are almost 10 years apart).
Note that U-212 was never offered as an option to a navy. When it was offered to the Italian navy, there was no U-214 yet.
U-212 uses an imported combat system partially made in Norway by Kongsberg, known as MSI-90, while U-214s combat system is made in germany.by Atlas-Elektronik, being the latest version of the ISUS-90 system.
There are many differences in combat systems, but one of the most important results in U-212 being only able to fire torpedoes, while U-214 can fire both torpedoes and submarine launched sub harpoon missiles. This will change in future versions of U-212 though.
The consolidation of german naval industry ended with the competition between both models in the 1990s.
One cant just say which of them is better. The U-212 was an absolute german need for the Baltic conditions. Italy wanted an AIP submarine, and there wasnt really any real choice at the time. When a navy makes an option for a model, the most logical option is to stick to it, and thus Italy is going to get an additional two U-212.
For a navy that is going to protect shallow waters, there is no doubt about the clear superiority of U-212. In deep sea operations away from the shores, U-214 will fare better.