A proposed Empire submarine program would have given Australia, New Zealand, India, South Africa, and Canada roughly twenty to thirty boats each, built up during the 1920s. The Washington Treaty imposed no submarine ceiling, leaving room to establish crews and operating experience as well as acquire boats. A larger force could have patrolled the Indian Ocean, reinforced Singapore, and threatened Japanese invasion shipping and logistics, although these are counterfactual possibilities. Submarine technology developed in uneven advances, with the need to master an existing generation offered as one possible explanation for pauses between improvements. Britain was investing in ASDIC while politicians and some admirals still hoped to abolish submarines by treaty. That preference, combined with concern about future designs, discouraged investment in a capability that remained available.
Notable Point · 29:44-40:57
An Empire submarine force outside treaty limits
The absence of a Washington Treaty submarine limit offered the Dominions a route to build local underwater forces and Pacific defenses.