Cannot be a rocket to aid in take-off as it is pointing upwards...
In late 1939,a proposal was made by a technical officer of KG51 to fend off attacking fighters from the tail of the bomber and reconnaissance aircraft, by installing a flame thrower.
The flame and smoke would effectively blind the pursuers by throwing smoke, dirt, grime, oil, etc. onto the windscreens.
In February 1940, experiments were done with He 111 and Ju 88 at the Tarnewitz test site.
It was used by KG51 at the start of the Russian campaign, but it was not successful.
There are known photos of the Ju88 set-up...