A trilogy, perhaps?

this might be too overambitious at this stage, but it might be worth concidering.

say there was to be a trilogy.
the first part could be the nazi ww2 operation, the second one the soviets or the us during the cold war (probably the soviets concidering the brainstorming idea regarding documented mail exchange between DDR and the USSR about what the nazis tried to find, great idea!), and the third one set in a future where europe has lost its powerful position.

to link them all together, we must introduce a lure other than the aryan origins at least as soon as in the second part. Such as a powerful tool/weapon/wealthbringer. I'm thinking that if some parts of my idea written below is going to be used, the treasure later search teams are after are the forbidden fruits of the tree in eden (that just brings destruction and torment, really, but noone will realize that).

A nice roundup of my previous idea would be that there's just one or a few survinging the ordeal, and that they manage, at last, to dispatch a message to the outside world: "We've found the forbidden fruit." Then the leaders of the third reich would know at least something about the first missing u-boot. which the soviets would look after. and then the students which Gert-Jan mentioned in his idea.

In all three parts, a mighty empire is desperate for more power (be it propaganda value (first film) or a turning point in war (second film) or in economic competition (third one)), and in the end, the individual has to suffer.

The good thing with this trilogy-setup is that the first film will need least resources. a bunch of actors, some props, a pair of blue blankets, 3d-rendering for the boot's interior/exterior, and a bunch of scenes in atlantis. I'm sure a soviet adventur would generate more 3d-rendering work. The same for if the storyline is that they're building a new boot from old blueprints. In other words, the project could grow part by part of the trilogy.

EDIT:
It could also be three movies put in another way one fore atlantis and one for hyperborea where atlantis focuses on discoveries with references from the bible (exile from eden, tower of babel, noah's ark), Hyperborea whith references from norse mythology (such as raganrök, fenriswolf etc), india and tibet (references from hindu writings such as kali yuga -the darkest of all ages - shiva, the swastika's origins etc etc) - all three has played an important role for the myths that inspired the whole mindset of the third reich and also later neonazi movements. Just an interesting thought, i think.

4. Nazi germany desperately needs solid ground for their propaganda

I developed this for synopsis number 2 but it became something else as I'm stuck in my own wheeltracks. Here it goes:

Short descripition: (edit 7)
One or a group of u-boots (1 to 3 perhaps) are sent out to a/several location/s on order from Himmler's SS Research departments via NSDAP where they hope to find the origin of the 'aryan race' in the sunken city of Atlantis (part of edit 9: and/or Hyperborea) in order to proove its supremacy. The sub which the film will focus on gets adrift and loose track of where they are and will find atlantis where they will have to struggle for survival, and eventually sanity, while carrying out their orders)

Protagonists:
Either the u-boot ordinary crew or the scientists onboard

Antagonists:
As above but reversed.

Mission:
Search for the origin of the aryan race by finding atlantis and, if possible, secure scientific proof of the supremacy of the same.

Possible outside threats (in suggested order of appearance and maybe depending on what year it takes place):
1. Destroyers, fighters
2. Mysterios underwater stream/power source (edit 6: and giant squids!! <-- contribution from my girlfirend)
3. Unrepairable engines, non-functioning means of communication, loss of fuel
4. Diminishing food rations
5. Unstable structures, maybe even traps, maybe hostile temperatures.
6. Some kind of (possibly imagined) 'beast' that lurks around (as mentioned in the general ideas task: an uncertain manifestation of the serpent from the bible)

Conflicts
1.Scientists (whom captain and especially crew must obey in most respects) are determined to succeed at all costs - crew is concerned about surviving and how to get home
2.See Story development number 3.

EDIT:

Storyline development:
1. They find a deserted atlantis; a crumbled city which is in most respects totally lifeless, complete with ruins, remains, gizmos that don't work, eerie atmosphere
2. Carvings, paintings and such explain the rise and downfall of atlantis, won't mention all too much to proove nazi theory but instead be a version of the fall from eden and similiar occult and religious beliefs. I'd like to leave a lot of the conclusions to be done by the audience so all isn't all too clear what it means, but that's maybe no necessity.
3.Different individuals could make different conclusions from what they find which could build up the conflict even more.
4.Conclict results in a few deaths on both side until conflict between the groups are solved in some way
5.What remains of the whole crew finds a way to survive for an uncertain period, whithout hope of ever getting in touch with the world above again or getting away, and because of the circumstances the question appears: Is this a life worth living? (I'd like to underline this by letting a member of the crew who's a very orthodox national socialist commit suicide because of the disgrace of failing the mission, which he believes must be concidered as a betrayal of not only the party and the army code but the whole german people and the reich due to the importance of the mission).

EDIT 2:
Self-comment. The main theme running through this mankind and the search of it came from, who or what made us or who/what made us evolve and become what we are. This is nothing unique in itself but i don't know anyone who's tried to write such a story from the perspective of people who more or less are under the influence of a world view constructed by the propaganda machine of NSDAP (or any other ultratotalitarian regime).
This difference makes it possible to explore, tell and ask things & subjects based on a very diffent mindset (which is a very intriguing spice).

EDIT 3:
Atlantis could actually be physical/non-spiritual counterpart to a lot of biblical stories. Examples:
-The tree of Eden from which the first humans ate the forbidden fruits of knowledge could stand right there. wether it is actually a tree (a mystical approach) or not is up for debate. An interesting approach would be to make it a symbol for the knowledge about property and warwaging: when mankind went from hunting/gathering to agricultural society, this meant we had resources to store which also led to the first motivation for organized warfare (plundering goods).
-The tower of Babel (with a twist, perhaps: a research center, university, library etc in the shape of a tower where people became so specialized in profession and language, needs and fears that they couldn't understand each other anymore which puts an end to whatever measure of political consensus or respect for political diversity they might have achieved)
-the construction site of noah's ark (from where people presumably have fled atlantis during its destruction to populate other parts of the world - with destruction i mean the destruction which the residents of atlantis have inflicted upon themselves through misuse/abuse of technology, power, resources, and themselves).

EDIT 4
(changed and further explained/developed some ideas in the previous edits)

EDIT 5
It is my intention for the whole scenario above to tell the audience how easy it can be to make assumptions based on earlier beliefs without it necissarily being correct (and exactly what is correct in this case might not even be displayed), as the most NSDAP-orthodox members of the group will try to explain all they see from a national socialist point of view.
Nazism is very far from what many believe but is at the same time a very well known package of ideas and is therefore the perfect background for such a storytelling, but its message could actually be rendered throgh any ideology, religion or cultural wave.

EDIT 8
On Ariosophy (the belief in that aryans were the crown of the creation, among other things): NS realistic politics aimed for good relationship with the church and Hitler himself is said to have despiced ariosophy and the mysticism it was surrounded by. Nevertheless, both the SS rune and the Swastika was borrowed/inspired from/by that movement. Many of the Ariosphists (whos ideas was a foundation for the NS ideology and who helped form NSDAP) was later sent to concentration camps. 1945 was not so much of an end for ariosophism as 1933 was as NSDAP saw to eradicate many of its followers as soon as they came to power. Nevertheless, the search for proof of aryan supremacy sounds pretty likely, especially as Rudolf Hess (Hitler's deputy) was deeply involved in ariosophism and Heinrich Himmler (head of SS) spent a lot of time with ariosophist friends. Not to mention that ideas from the movement was concequently used in propaganda alonside with normal party blaha and use of christian beliefs.

More material on that matter (haven't read it through yet but will asap):
http://en.wikipedia.org/wiki/Ariosophy

EDIT 9:
Story detail: If we assume the party sent out multiple submarines during the operation, it is probable that one was sent on expedition to 'thule', supposed polar homeland of the aryans (a theory which former SS man Willhelm Landig revived in the 70s. This whacky dude also made up a story about a mysterious power source which would regenerate the aryans, aswell as he popularized pre-nazi ariosophist theories about atlantis and other stuff). In earlier movements that tried to explain where 'aryans' came from, hyperborea was a hot tip. it is in many respects esentially the same.

http://en.wikipedia.org/wiki/Hyperborea

This opens up for some questions: Is this story skeleton meant to take the crew to atlantis or hyperborea? on what should the storyline put its focus on?

A few comments

A few comments on synopsis ideas number 1 and 3: these could, besides having the potential of becoming interesting movies in their own right, also be a great way to make a sequel if idea number 2 will turn out to be the best way to go.

A little concern about a rescue-mission-based synopsis: It was more of a rule than an exception that u-boots did sank without anyone knowing the reason for sure (due to restricted means of communication) - and later, as far as i know, it was concerned to be a necessary sacrifice: if a boat sank, was shot asunder or had major malfunctions, noone would look for them. But, on the other hand, if the goal with the mission is to by scientific evidence proove the supremacy of the 'aryans' and therefore in some respect justify the ideology which would have world-wide political concequences, they'd probably put more effort into succeeding and investigating any failed attempts including missing and/or derelict vessels + crew.