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In this docuмentary it is explained that at the start of WWII it was considered irresponsible for submarines to run surfaced during daytime since they could be spotted by the enemy. Subs remained submerged only to surface at night to vent the interior air and recharge the batteries. Being submerged in the daytime meant the subs could only move forward at the speed of a walking man and therefore would have to position themselves ahead of the target ships and wait for them to approach the submarines. Their attacks had to take place at close range, meaning a first strike miss was a very dangerous situation for the attacking subs. Trying to escape while submerged was very risky considering depth charges, and remaining surfaced, even though faster on the surface than ships, they were easy targets for the big guns on ships.
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Then, as the war progressed a newly developed plan using submarines for attacking surface ships during the daytime changed the strategy of subs. It was realized that at longer range a sub was not visible to a ship while the ship was visible to the sub, and a sub could outrun ships so long as the sub does not dive below. This meant enemy target ships could be followed at a greater distance. By their low profile, subs on the surface would remain outside the viewing range of ships (hidden by the earth's curvature) while the target ships' course and position was trackable because the submarines could watch the ships' higher profile and their smoke exhaust (even while the hull, decks and superstructure were hidden by the earth's curvature).
Topic: Why Do Periscope Views Hide the Lower Hull of Distant Ships? (Read 8644 times)