The Government of India produced these mugs during the Second World War and possibly earlier. This example is made in green enamel by Bengal Enamel in May of 1944. Note the soldered seam along the handle as well as the raised rim on the base.
In the field most soldiers eat ration packs or something equivalent. Behind the “front line” it is common to have food prepared, frequently at a unit level, by cooks and distributed to all the soldiers through a mess or canteen system. The Indian Army in 2WW was no different and alongside the mess tins issued for combat use, enamelled cups were used in barracks and other camps permanent enough to warrant their use.
Picture (left) from the CSS Museum.
Picture (right) from the internet.
Cup in the CSS Museum used by Sgt Ken Langridge in West Africa and Burma (Ceylon) during 2WW.
Bengal Enamel VIII, 1944 Bengal Enamel May 1944