The story
* jerry from jerry or Jerry. Similar to jerry-built or "jerry-sneak". Possibly taken from Jerry, a nickname for Germans. * jerrycummumble and its alternative jerrymumble possibly made to rhyme with fumble, rumble, or tumble. * Potentially related to "jerry-cum-fumble". * Its earliest documented usage is 1709, but Green's Dictionary exemplifies frequent usage of the term between 1785 and 1834.
Etymology from Wiktionary, CC BY-SA 4.0.