WWII

They used a J.

Jerry was a World War I British Army slang for "German," 1919, probably an alteration of German, but also said to be from the shape of the German helmet, which was like a jerry, British slang for "chamber pot" (1827), probably an abbreviation of jeroboam. Hence jerry-can "5-gallon metal container" (1943), a type first used by German troops in World War II, later adopted by the Allies. The German can was superior to the British or American and they adopted the German design.

And for the record: The Germans were called "krauts" by certain Americans (probably derived from "sauerkraut", although the Germans are hardly the only people to eat that), the French term was "boches" and the Dutch term "moffen". I am not aware of the etymology of the latter two terms.

You are correct about the name kraut being derived from sauerkraut.

Boche is a French slang word for rascal. It was first applied to German soldiers during World War One.

The Moffen was a Dutch slang word for Jerries.

It was suppose to be a deragotory term.

Quite a few Council (owned by the state) houses in Britain were built using German prisoners of war. Technically the war was over when these were built, but the German prisoners were not repatriated until the late 40's, or early 50's (quite a few wanted to stay on in England, Canada etc, funnily enough).
Many houses were bombed flat during the Blitz, and there were many thousands of people without adequate housing. By using the German workforce, many extra new homes were rapidly constructed, and these came to be known as "Jerry built".
If anyone refers to a Jerry built house, I know immediately that it dates from around 1950.

As far as I am aware, "Jerry" was more of a WW2 nickname, and although it was used in WW1, the usual term was "The Hun" or just "Hun".

There are some different explanations to be found online, like this one (as explained on Phrase Finder


Source

I remember having read somewhere that 'Jerry' was an old colloquialism for chamber pot and thus was alluded to the shape of an upturned German helmet ("Pickelhaube").

WWII Jerries or Gerries
Thank you all very much!!

MoragE

Walter, my friend (when I was a mere stripling) lived in a house that was built by German POW's, and the whole estate (possibly 100 houses) was mainly built by "Jerries". Their names were engraved, or chiselled in every hidden nook and cranny, and we used to spend ages, hunting around the house, trying to find another (mainly on exterior brickwork, high up and underneath the guttering, so we used binoculars).
Everyone referred to the estate as Jerry built.
In actual fact, I still have something in the Attic that was made by a German POW. It is a soft toy elephant, made of khaki blanket, and stuffed with god knows what.
It was given to my Nan, because she used to go out and help make cups of tea for the German workers. They couldnt buy anything, due to not having any money, so they used to make things to say "thank you" to the girls.
Her friend was given an exquisite wooden Chess set, which would probably be worth a pretty penny as a collectors item now.
I still think of those houses as "jerry built" though.