The claim that U-class boats were merely trainers does not fit their procurement history. The Royal Navy developed the design through prewar launches, then placed larger orders as war approached because compact boats could be produced quickly for the Mediterranean and northern European littorals. T-class boats addressed long-range Far Eastern ambush missions, while S-class boats filled a broader multi-role niche. This sequence also reflects a navy preparing under a government assumption that major war would not arrive before 1942.
Notable Point · 51:53-56:51
Why the Royal Navy built U-class submarines before wartime demand peaked
The U class was an operational coastal submarine developed before the war, not a training type improvised after hostilities began.