The quickest boil of water you can have, 7 minutes for 2.2 litres!!!! Using only a few leaves and twigs!
According to Wikipedia:
A storm kettle is a device used for boiling water in the outdoors. It consists of a base, in which a fire is lit (usually with wood, paper, etc.), and a double-walled main body. The centre of the main body acts as a chimney for the fire, while the water is contained in the chimney wall. A large surface area of water is thus exposed to the heat, little heat is lost directly to the atmosphere, and the centre chimney creates a upward chimney draft of heat, maximising water heating efficiency. A typical kettle can boil 2.5 pints of water in about 5 minutes. Typically, bits of paper, twigs and other small combustible material are started in the base, the kettle is put on the base, and additional burnable material is dropped dropped the chimney as needed.
Kettles of very similar design are manufactured by the Kelly Kettle Company (Kelly Kettle or Volcano Kettle), the Eydon Kettle Company (Storm Kettle) and the Ghillie Kettle Company. They are all manufactured from aluminum. Two or three sizes are available, from 500 ml (~2 cups or 16 oz) to 1.5 L (~6 cups or 50 oz). The manufacturers also sell a cook set with a little grill and pan that fits over the base. The Kelly Kettle Company also supplies a pot support which is placed in the chimney which ensures the effective use of the cook sets. The cook sets fit into the internal chimney for transport.
I've got a tin Thermette made in NZ, and a Kelly kettle made in Ireland. Although I havent used the Kelly Kettle yet (it must go under the Christmas tree), the Thermette is amazing! And if you PM me and ask nicely, I know where to get a Tin Thermette for only $50, brand new!