Gibber,
The T3 was superb bit of engineering theory, it was just let down by poor fuel control and monitoring systems. A flat 2 stroke supercharged diesel engine, each opposed pair of pistons shared a common combustion chamber. I think it was called reciprocating or something. With modern electronic control systems, it would be a winner today. And what a lovely smooth mellow noise they make.
Did you see the moving gif of one on the Dutch Commer site above?