If you know or suspect your jeep is ex British army, you can go on the RLC archives website. It costs £30 for them to look and they may not find anything. If they do, it will be what's called a key card. It shows the post war registration of two numbers, two letters, two numbers, the chassis number, the wartime M number (they weren't always painted on the bonnet) the contract number bought under, whether it's a Ford or Willys and other odd bits of information. Mine says it was sold off by the Ministry of Supply on 15/01/59. Unfortunately there are no unit records for mine. Some exist, but not always. The research is easy if you know the post war registration but it can be done by chassis number. The key card is sent by email as a digital copy.