The three British Royal Navy M Class submarines (M1-3) developed towards the end of the First World War were fitted with a deck-mounted 30.48-cm (12-in) gun, a weapon more commonly found in turrets on battleships. The diesel-electric powered submarines were 90.5 m (297 ft) long, had a surface displacement of 1,600 tonnes (3.5 million lb), and could travel at 8 knots (15 km/h or 9 mph) submerged and at 14 knots (26 km/h or 16 mph) on the surface. The gun and mounting weighed 129 tonnes (284,396 lb). The size of the mounting actually enhanced the submarines diving qualities - the weight helped to keep her down, whilst its volume stabilised the boat at periscope depth. M1 was famously lost with all hands in 1925, after a collision with another warship in the English Channel.