HORNBY OO BR, M7 Class, 0-4-4T, 30244 - Era 3HORNBY OO BR, M7 CLASS, 0 4 4T, 30244 ERA 3 Ideally suited to the demands of suburban workings with frequent station stops, the M7 possessed quick acceleration and good tractive power, equally at home on Branch line workings or acting as station pilots. Unfortunately, following a major derailment at Tavistock in 1898, the Class were withdrawn from fast passenger services, the 0 4 4 arrangement proving inherently unstable at continuous high speeds.