The period between the wars was an important one for British submarine development. It was a time when the Navy learned from its experiences in the First World War in terms of technology but promptly forgot any tactics learned. Our submarines went from being rather primitive, mainly small, coastal craft to being sea-going underwater warships, bristling with high technology and a superior trained personnel. It was also a time of tragedy with many submarines lost to accidents - from the sinking of the M-2, a large aircraft-carrying submarine in 1932, to the tragic loss of HM Submarine Thetis with the loss of one hundred crew, just before the Second World War.