Quoted underwater range only makes sense at its associated speed. Battery endurance fell sharply as speed increased, so a boat driven hard could exhaust its stored power far sooner than a low-speed figure implied. Salt-water contamination could make the battery problem still more dangerous. Submerged movement therefore had to be rationed, which made patrol position and ambush geometry especially important.
Notable Point · 25:22-26:31
Underwater speed rapidly consumed submarine endurance
Diesel-electric boats could not convert their quoted low-speed underwater range into a long high-speed chase or escape.