However I've also seen it spelled jury rigged . It's much older than World War Two. It refers to a mast which is makeshift or a temporary contrivance, perhaps because the original was lost or damaged in a storm.
Nobody knows for sure where it comes from.
Neither has been substantiated, I'm sorry to say. It's possible that the confusion between jerry and jury is much older than we think and that jerry in jerry-built is actually a corruption of jury , in the modified sense of 'inadequate' rather than 'temporary'. And, of course, Jerry has yet another meaning, the one you referred to in your question, an informal version of German , hence jerrycan . These three terms have got thoroughly mixed up in people's minds, to the extent that we may never be able to disentangle them again. All rights reserved.