Development proceeded from individual trial boats through the Odin, Parthian, and Rainbow groups instead of producing one finished solution at once. Each order incorporated lessons from its predecessors while retaining the long range needed for Far Eastern service. Nineteen boats were oriented toward that work by the early 1930s, a substantial commitment to the theatre. Their size made sense for long Pacific transits but was much less attractive in confined Mediterranean waters. Heavy wartime losses in the Mediterranean illustrate the cost of using theatre-specific designs where they were poorly suited.
Chapter · 29:13-31:47
Building a Far Eastern submarine force by iteration
The O, P, and R boats emerged through successive experiments to give Britain long-range submarines for the Far East.