Surprise! I found my reference! bad thing, I have to trascribe the cite from the book, so pardon me for any typing errors.
Anyway.
[QUOTE=Zeppelin! The German Airship History]
“Meanwhile, various proposals had been made to build a fleet of sixteen Zeppelins and to organize an ambitious multi-national service, but these came to nothing because clearance for the sale of its (non-flammable) helium was not granted by the US goverment.”
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[QUOTE=Zeppelin! The German Airship History]
“LZ 130 was ready to take off on 14 September 1938 and, following Dr Eckeners recommendation, was, like LZ 127 named Graf Zeppelin. The United States was at the time the only country producing helium, and it gave a special permission for LZ 130 to be inflated using this gas - thus requiring the ship to be modified. However, before the gas was sent to Germany, the US Goverment found itself under domestic pressure to reverse the decision as a protest against Germanys National Socialist regime, and the agreement duly terminated. LZ 130 had to be converted once again to accomodate the more dangerous hydrogen.”
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[QUOTE=Santos L Halper]
Yep, Indiana and his father escape from the German zeppelin via a deployable airplane. In the real world none of the German airships had this ability (I don’t know if they ever even seriously considered the idea. The US rigid airships Akron and Macon actually did carry several biplane fighters and got very good at deploying and retrieving them in flight.
Cites: one two three
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The answer is, once, for five minutes in 1936… 
[QUOTE=Zeppelin! The German Airship History]
“On 27 April 1936 LZ 129 (Hindemburg, Ales note) participated on an experiment undertaken by Ernst Udet to test an idea for speeding up airmail services. Udet had taken off at Darmstadt-Friesheim in a small FW 44 Stieglitz (D-EUTE), a large hook fitted to the center of the biplanes upper wing. The Hindenburg, commanded by the experienced Max Pruss, approached the aircraft from its Frankfurt base at an altitude of 700m. The first attempt at a connection failed but the second approach was more successful, Udet`s Stieglitz hooking itself under the vast hull of the airship. After about five minutes the aircraft was released again and returned to Darmstadt.”
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It doesn`t say more about that, but apparently there where no further developments.