Triumph of the Will was distributed by UFA. Prior to the Nazi takeover of film in Germany, UFA made a science fiction film F.P.1 antwortet nicht (lit "F.P.1 doesn't answer"). The movie about a race by an idealist, Lt Droste to create a floating platform in the Atlantic for air travel being sabotaged by less-inspired industrialists and political types. Meanwhile Drost, his friend Ellison (a flying ace) and Claire, who owns the docks the plans for the floating platform were created in have a romantic triangle to sort out. A big success, the film inspired an insult to Hitler where he was referred to in the early days of his rise to power as "P.G.1 antwortet nicht." (meaning "Parteigenosse 1 antwortet nicht," or "Party Member 1 doesn't answer.") Maybe you had to be there. But I imagine Hitler took some satisfaction when he took over UFA and had them put out Triumph...
F.P.1 was directed by Karl Hartl, an Austian who remained working for the Austrian arm of the German government when they nationalized UFA. Hartl returned to directing post-war in Austria and did so until the early 60s. He died in 1978.
F.P.1 starred Hans Albers as the flying ace (who went on to do another sci-fi film that squeaked under the Nazi control, Gold). Albers also stayed in Germany, but as a big star he never endorsed the Nazi party. Albers, after the end of WWII and unlike many actors who stayed in Germany, was able to find work even if in a much reduced fashion, usually in wise old man roles. Partially this was due to his early popularity, partially because he never endorsed the Nazi party and partially because he had a Jewish partner, Hansi Burg. While they stayed partners during the war, for her safety he got her to Switzerland; Albers was so popular he didn't get blacklisted even though the Nazi's knew of the relationship. He died in 1960, having become increasingly dependent on alcohol.
His female lead was Sybille Schmitz as Claire. She also stayed in Germany during the war, but post-war her career never recovered despite the fact she had a contentions relationship with the Nazi run film industry. Finding few film roles and spiraling in drugs and depression, she committed suicide in 1955. The third lead, Droste, went to Paul Hartmann. He too stayed in Germany, and like Albers he continued to work after the war through 1969 (and appeared in the 1962 film the Longest Day). He died in 1977. Peter Lorre had a small part as the photographer friend of Albers; Lorre famously fled Germany, first to England and the to the US where he had a long career as heavies in dramatic and comedic roles. Similarly writer Kurt Siodmak, whose book the film was based on and who co-wrote the screenplay, fled Germany, ending up in the US where he changed his name to Curt Siodmak and wrote and directed a veritable 'who's who' list of films that would be recognized by Monster Kids (including The Wolf-Man and I walked with a Zombie)
F.P.1 like other big productions in the early sound period was made three times. Once in German, once in French and the Second in English. The French version, called I.F.1 Ne Répond Plus stared Charles Boyer as Ellison. Boyer was already an international star, starring in films made in several countries. While he enlisted during the early part of WWII, he was discharged to make films in the US as it was believed that would support the cause better. He would continue acting in films into the mid-70s. In declining health himself, he committed suicide after the death of his wife. Claire was played by Danièle Parola who made several films in multiple countries in the late 20s and 30s. She was married to actor André Daven and died in 1998. The role of Droste went to Jean Murat who continued making films through the war for France and into the 1960s. He passed away in 1968. The French version of the film is considered lost.
The English language version of the film ended up being a much shorter film than the German original. It was released as F.P.1 in the UK, then reissued as Secrets of F.P.1 and released as F.P.1 Doesn't Answer in the US and Where the Light house Shines Across the Bay in Australia (literally WTF Australia?) and starred Conrad Viedt (Cesare in Das Cabinet des Dr. Caligari and Gwynplaine in The Man Who Laughs) stars as Ellison. Viedt had a long career in German and UK film, but died young due to a congenital heart condition in 1943. Jill Esmond, Laurence Olivier's first wife, stars as Claire. Her acting career slowed down after Olivier and she divorced so Olivier could marry Vivian Leigh; presumably this was as she had to take care of their son. Olivier and Esmond remained friendly through the rest of his life, and he never stopped paying her alimony. Their son recalls her writing to him late in her life that she still loved Olivier despite everything. She died in 1990. Leslie Fenton played Droste; Fenton was born in the UK but his family had emigrated to the US when he was young. He made many films in the 20s and 30s before becoming a director. His second career was cut short by WWII where he joined the Royal Navy Volunteer Reserve and was wounded during Operation Chariot. Post war her returned to the US and directed a few more films before retiring in the late 1950s. He died in 1978.
So all this is the wind-up, but given the Nazi-era film stuff, I thought it might be interesting background. I watched the Secrets of F.P.1 version of this film. Its definitely early sound filming, and I think the shortened running time particularly hurts understanding the relationship triangle between Ellison-Claire-Droste and I think makes the motivations of the saboteurs less clear. But its an engaging early film anyhow, and other than a few quibble about things not being clear in the film, worth watching I think.