Military canteen cups are not particularly efficient. Use a Primus Tea Kettle (wide hard anodised aluminium base) and use 2x14 gram Esbit Tabs. Use a wind screen as well such as a titanium foil or the heavier Aluminuim type.

You might just be able to boil enough water (800ml) for a Mountain House and a cup of tea with 2x14 gram Esbit tabs.