More escorts at the start of the war could have inflicted losses while enemy submarine forces were still small. Losing experienced crews would also have removed personnel trained during the interwar years. The comparison is with German destroyer losses at Narvik and the disruption caused by losing ships and experienced men together. The proposed effect on submarines is counterfactual, but it explains why an early loss could hinder later expansion more than the hull count alone suggests.
Notable Point · 1:46:51-1:47:45
Why early submarine losses could matter beyond hull numbers
An escort reserve could have threatened the experienced crews needed to expand wartime submarine forces.