Following Submarine Matters' German vs Swedish Advanced AIP for Submarine Sales to Poland, the Netherlands and India of September 16, 2019, Anonymous has kindly provided the following comments on the Type 212CD under development for the German and Norwegian navies.
Anonymous (with some editing and comments by Pete)
Information on the Type 212CD (Common Design) is limited. The 212CD:
i) is a Norwegian-German TKMS joint development with Norway purchasing 4 and Germany 2. Deliveries are expected in 2016 . The 212CD are based on the Types 212A and 214
ii) will have a displacement of 2,400 tons [source? displacement not in 4 . This is similar in size to the Netherland’s Walrus-class (see Table in , displacement of 2,400-3,000 tons, [or less see right sidebar] and hull is made out of non-magnetic steel ,
iii) will have extended range, speed and endurance(6 to 8 weeks)  [3, 4]. Hence it will use two MTU 12V 4000s because just one diesel (used in the 212A) is not suitable or safe for long range operation. To accommodate the two MTU diesels the beam/diameter has been enlarged to 8m. This is an increase from the 212A 6m beam useed for just one MTU 396 diesel
iv) use of SAFT made lithium iron phosphate batteries (LFP) is likely [source?]. This is more stable [than other LIBs and/or more stable than LABs?] at the low Baltic and North Sea, North Atlantic and Arctic Ocean temperatures the 212CD will operate in.
v) The latest Permasyn magnetic propulsion motor will be used.
vi) As with the 212A and 214 for safety the AIP oxygen tanks and hydrogen cylinders are outside the pressure hull and inside the light outer hull. The 212CD will use fourth generation fuel cell (FC4G) AIP
vii) Italy, the Netherlands  and Poland could buy into the 212CD program (does it satisfy their requirements?) . But, published data on 212A and 214 may provide some important information on 212CD .
 “The Royal Netherlands Navy’s Submarine Replacement Programme”, European Security and Defense, May/09/2019, https://euro-sd.com/2019/05/articles/13140/the-royal-netherlands-navys-submarine-replacement-programme/
“The Type 212CD followed the [curtailed Type 212NG (Next Generation) program], a design by tkMS for the German Navy. In turn, the NG was derived from the Type 212A and the Type 214. When Norway joined the programme, the requirements were merged into a new design: Type 212 Common Design. Not much has been disclosed about these submarines, except that their displacement is 2400 tons and their hulls are made of amagnetic steel.”
 “German-Norwegian Type 212 CD submarine contract to be signed early 2020”, NAVAL TODAY. COM, Jun/014/2019, https://navaltoday.com/2019/06/14/german-norwegian-type-212-cd-submarine-contract-to-be-signed-early-2020/
“The new Type 212 CD submarines will share the low signatures of the Type 212 boats in service with the navies of Germany and Italy but will have extended range, speed and endurance to allow worldwide operations, according to TKMS.”
 “U 212 CD, the next Norwegian submarine, but what for? (1/2)” , DefenceChronicles, https://www.defencechronicles.eu/u-212-cd-the-next-norwegian-submarine-but-what-for/
“Of course, in terms of the RNN submarines’ capabilities, the Norwegian Sea surveillance mission is very demanding since they must keep submerged almost permanently in sectors of the North Norwegian Sea or along some fjords. This requires endurance at sea (6 to 8 weeks), keeping watch in a patrol area between two long dived snorkeling transits on the way out of the home base and on the way back.”
 “U 212 CD, the next Norwegian submarine, but what for? (2/2)” https://www.defencechronicles.eu/u-212-cd-the-next-norwegian-submarine-but-what-for-22/
“By selecting the U 212 German class, the Norwegian MOD made certainly the best choice of a coast guard submarine, while objectively giving up the ambition to extend its Navy control to the open Norwegian Sea and play a combined role with other friendly ocean going submariners, in the hunt for the new “Red Octobers”. Also see Table.
 “German, Norwegian officials huddle over joint submarine program” https://www.defensenews.com/global/europe/2019/04/30/german-norwegian-officials-huddle-over-joint-submarine-program/
“The design of the new boats has yet to be locked down, which may reflect a last glimmer of hope in Berlin and Oslo that other countries in the market for submarines — namely Italy, the Netherlands or Poland - could join the effort.”
 The TYPE 212A is a small and stealthy submarine design. Both oxygen tanks and hydrogen cylinders are stowed outside of the pressure hull on [safety grounds]. In line with the stealth, extensive use is made of non-magnetic steel, supplemented by lightweight [graphite fiber reinforced plastic] GFRP for hull outer coverings and the fin. TYPE 214 is described as an evolution of the TYPE 209 with the addition of a number of innovations found in [later model 209s].
Pete Comment: I estimate "2,400 tons" displacement for the 212CD for the Norwegian and German navies to be too high for the shallow Baltic. Perhaps 2,200 tonnes submerged may be more accurate. This is similar to TKMS latest launched 2 or 3 diesel Singaporean Invincible (was 218) class. The Invincible/218 for the shallow Malacca and Singapore Straits is estimated at 2,000 tonnes (surfaced), 2,200 tonnes (submerged). The 212CD is likely to have X-plane rudders (below) like the 212A and Invincible class. The the photos of Invincible/218 model above and below may be most like the future Type 212CD.