Ok, here's a seperate thread w/ spoilers.
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There, now you can't complain.
Theories on what happened? If I recall correctly, the Xindi homeworld was described to have been destroyed 200 years earlier. From a story perspective, it would be cool if (since the 1940s are 200 years before Enterprise) the following story develops:
1. Vortex travel can = time travel, as shown in the earlier episode with the beaten up old NX-01.
2. Destroying the Xindi Weapon or the Sphere network screwed up vortex travel, and the Aquatic vessel (w/ Enterprise) was thrown back in time.
3. They are at the time right before the Xindi planet was 'destroyed'.
4. The alien nazi was an 'Avian' Xindi, and the Avians are foot soldiers in the 'Temporal Cold War' story arc.
5. The Aquatics are the actual preservers that manage to save some number of Xindi before Xindi Prime is destroyed as part of the temporal cold war, and they can't rescue any Avians because the Avians are active bad guys that are trying to kill the Enterprise & Aquatics. In the process of rescuing people, the Aquatic vessel is destroyed and the whole 'sphere-builders as preservers' myth is set up.
Of course, the Nazi alien could also be a Reman from Star Trek: Nemesis and he's using his mental abillities (established in the movie) to make everyone think he's just another German, but he's actually Hitler's aide.
Oh, and I'll head the wags off at the pass by pre-emptively stating that yes, I'm a 'geek' and some people might actually call me a 'dork', but the real question is, if I'm so un-cool, why are YOU reading the thread? ha ha! parry, thrust.