The thermette, patented by Auckland electrical engineer John Hart in 1929, provided a quick and easy way to boil water outdoors. It comprises a cylinder surrounding a conical chimney on a stand that contains a fire plate. The cylinder holds water, and the tapered chimney heats the water to boiling point very fast. The contained fire allows the thermette to be used in all kinds of conditions.

When the Second World War broke out in 1939 the New Zealand army asked Hart to waive the patent so it could make its own thermettes. He agreed, and the device became standard issue to units; soldiers dubbed it the 'Benghazi boiler'. Although the thermette is often used as an example of original New Zealand design, its concept was similar to 'volcano kettles', made by Irish gypsy tinsmiths since the mid-19th century.