What is the fine-grained topic of the following text: The Alvis group of companies, comprising Alvis plc (London, UK), Alvis Vickers Ltd (UK), Alvis Bridging Limited (UK), Alvis Hagglunds AB (Sweden), Alvis Moelv AS (Norway), Alvis OMC and Alvis Gear Ratio (South Africa), is one of the world's leading manufacturers of armoured vehicles. Only return the topic.
Alvis group of companies as manufacturers of armoured vehicles