CONTAINS ZE SPOILERS
....though, curiously for a film calling itself The 25th Reich, setting itself in 1943 and utilising that German-looking Iron Sky font on the DVD artwork, it doesn't actually contain very much in the way of Nazis. Rather it's a (very) small-scale men-on-a-mission war movie with just five characters and a sense that it was deliberately constructed to recall war movies of the time (except for the swearing and, er, CGI spaceship).
A small platoon are on a mission to track down two escaped pumas in the Australian outback (for reasons too dull to go into here), using a huge machine to attract them. In fact it's a top-secret mission to find a flying saucer and stop it falling into the hands of the Nazis, and the machine is actually a time-travel device. But, after a ton of backstory and waffle, there might be a traitor in the ranks...
Towards the end it stops being mildly silly and opts instead for colossally silly, as our heroes are thrown forward into the far future where the Nazis are planning to spread their hideous creed across the entire universe with a fleet of spaceships, and any dissenters are chased down by loyal Nazis who have been converted into giant mechanical spiders. Sadly by that point the film has crossed the line between endearingly dumb and just plain stupid, so it doesn't fly even on the mythical so-bad-it's-good level. The giant spiders are actually pretty decent monsters, with better CGI than the retro spaceships, but it's too little and way too late.