I did some checking and there were tinned canteens. Probably all will be dated 1942, possibly 1943 as evidenced by my cup. 1941, early 1942 will be aluminum, 1942 starts the tinning which was a failure that led to the porcelain in mid 1942 which again was replaced in 1943 with aluminum again and then finally stainless steel.

I do not have a 1941 canteen, four 1942's either aluminum or porcelain.