The limited offensive potential of individual U boats was compensated for by the considerable number that were commissioned in a short period of time, and these small and nimble vessels became one of the most important operational classes in the Second World War, with a record that can fairly be. described as heroic.
The wartime submarine fleet relied almost entirely on the S, T and U Classes. This policy was very different to that of the First World War (when some 12 new classes had been. developed), and was pursued so as to cause the minimum interference with the shipbuilders' production programmes.
The majority of the 49 commissioned U boats (all but two of which were built by Vickers) served with the Second Flotilla
