Think of the US army in action and chances are a khaki-coloured Hummer truck will come to mind. The High Mobility Multipurpose Wheeled Vehicle, to give the souped-up truck its proper name, is one of the most widely recognised in the world and the US army has about 150,000 of them. But Hummers can roll over, killing and injuring soldiers on the battlefield and at home. Now the British engineering group Ricardo is helping the US defence department to make its Hummers safer by installing devices that keep the trucks stable. Stable profits: Ricardo makes devices that prevent the US army’s Hummers from rolling over