...the civil sector won't use them (i.e. round tins)as they take up more room during shipping
S'funny. All the cans of engine oil that I ever poured into an engine were round and opened by punching triangle shaped holes into opposite sides of the lid with a key that had another end that was useful for opening bottles. Oddly enough, I noticed the chap topping up the hydraulics was using exactly the same key to open his cans of hydraulic fluid.
But we're civilians so what the **** do we know?