The first thing that struck me in the description of this film was the word 'volunteers' in inverted commas. The Communists weren't the only ones who had volunteer units in their ranks and it can be safely said the The Condor Legion was comprised almost exclusively of volunteers.
The film itself is unusual by virtue of the fact that it's not a WW2 documentary for a change and, for once, it gives the winning sides account of the Spanish Civil War. Hemingway et al have monopolised the history of that era for eighty years. Now, at last, we see the other side of the story.
As with most war documentaries, it gets a bit tedious with explosions, men firing rifles at unseen targets and bomb after bomb hitting the ground. Karl Ritter, the director, almost certainly used some recreated scenes to fill in parts of the conflict that were difficult to film, the scene where a German spotter plane gets intercepted by Republican fighters being the most obvious one. Scenes where troops storm strongpoints are equally suspect but every war documentary director has done the same thing since WW1.
I found the most interesting parts of the film to be Condor Legion's return to Germany, disembarking in Hamburg and then on to Berlin for a review in front of Goering and a speech by Hitler. Other interesting sequences include the rapturous reception given to liberating Franco forces in various Spanish towns and cities, so much for Franco being "unpopular".
One unforgettable scene in the film is the questioning of captured members of the Communist 'International Brigade', including black members of the Abraham Lincoln Regiment and a rather chirpy sounding Welshman who basically implied that he came to Spain to fight because he was unemployed! What happened to these men? Neither side showed much mercy in what was a vicious ideological war.
I enjoyed the film. Together with Russell Palmer's 'Defenders Of The Faith' it's one of a handful of cinematic records of the Spanish Civil War from the Falangist perspective.