1 Monty: Well dad, on our way to Geneva by zeppelin. That was a close escape.
2 Haken: Der is Herr Doktor Jones! Nach ihm! Schnell!!!
3 Prof. Jones: {being chased by Nazis} Junior, how about we escape on the plane attached to the underside of the zeppelin?
4 Monty: German zeppelins never carried planes, dad! This is real history, not a movie!
4 Prof. Jones: Oh, the humanity!

2012-01-18 Rerun commentary: And there go the backgrounds again. They must be flying through featureless cloud.

The idea for this strip comes of course from the scene in Indiana Jones and the Last Crusade in which Indy and his dad escape from the German zeppelin by stealing the small plane attached to it. In reality, the Germans never operationally used airships with attached planes after the end of World War I in 1918. The British and Americans, however tried it several times, and the most successful implementation was with the American airships USS Akron and USS Macon, which carried 4 and 5 F9C Sparrowhawk biplane fighters respectively. Both airships served the US Navy well as flying aircraft carriers, until they were destroyed in crashes in 1933 and 1935, ending the era of airship-mounted planes.

In early 1937, just a couple of months before the LZ 129 Hindenburg's fateful last flight, the Luftschiffbau Zeppelin company experimented briefly with fitting the ship with a trapeze system for a parasite biplane. But the trial was unsuccessful, and it never flew operationally with the plane attached.

So Monty is slightly incorrect in the comic. The Germans did have zeppelin with a plane attached in reality, but it was either about 20 years earlier than the setting of this strip, or only a short experimental trial.