The British Rail Class 373 or TGV-TMST train is an electric multiple unit that operates Eurostar's high-speed rail service between Britain, France and Belgium via the Channel Tunnel. Part of the TGV family, it has a smaller cross-section to fit within the constrictive British loading gauge, was originally able to operate on the UK third rail network, and has a lot of fireproofing in case of fire in the tunnel. This is both the second-longest——and second-fastest train in regular UK passenger service.