That is a very nice bottle. I have one painted in tan and Karkee has a nice one in galvanised metal as well; this is the first green one I have come across. They are not common and yours looks to be in lovely condition, complete with stopper.
They would have been used by all Empire forces in the far and midle east (basically anyone who was closer to India for supply than the UK), so British, Indian and African troops and also probably the Chinese Nationalists equipped by the British Empire.
Although the origin of these pressed steel "ML C. T. 1943" waterbottles is unconfirmed, Indian manufacture does seem likely. The shape of the spout is similar to that on Ed's bottle as well as post war bottles made by Bengal Enamel and Madras Enamel. I'm not certain if it was made by Metal Box, since the markings seem to differ, but it's certainly possible!
Congrats on a very rare bottle!
I cant recall ever seeing these around but lately ive seen quite a few...I now own four!The first one I found I bought hoping it was the Aluminium 1939 type....it wasn't.
There is one on wdmilitaria but the description states he's 'always believed them to be of Indian manufacture'...
Ive heard a possibility that these bottles could be American lend-lease?Too well made to be Indian!There was about 30 of these for auction locally to me recently.
There do seem to be a lot of these bottles on eBay at the moment. I hadn't considered a US origin...intriguing!