U-Boat Question.?

Question

Since sonar was invented by the Allies during WW2 how did U-Boats find ships to destroy. How did they navigate?

I saw a movie where the U-Boat had some kind of electronic device. It wasn't the circular shaped 360 degree ones though. It had lines that went straight across like a heart monitor or something.

Answer 1

in addition to the other posters

many of the freighters used in WW2 were left over form the WW1 era....there were little or no ships built during the Great Depression, so most of the hulls...and engines....were 30plus years old.

Old engines ( for diesel powered ships ) make smoke. Old boilers ( for steam powered ships) make smoke. Old boilers fired by coal.and there were still a lot around in 1939-41 make smoke.

Almost all merchant ships traveled in convoys. "Fast" convoys did 10 miles an hour. "Slow" convoys did barley 7.
Put 30 or 40 or 50 ships together, each making a little smoke and it all adds up to a fair amount of smoke on the horizon.

U-Boast patrolled on the surface, They would see the smoke and move into the attack. In the Pacific, US subs called this "the end around".they would sight smoke, figure out the convoys course and speed , and run at high speed about 10 miles off to the side, around to where the convoy would be, dive and then .........boom!........

The flat line device you saw is probably the screen for the Biscayne Cross.... a cross shaped radar receiver antenna would be deployed while running across the Bay of Biscay to and from the sub ports in France, or whenever on the surface; when a radar beam from an Allied destroyer or plane would hit it you'd get a blip on the flat line and it would be dive dive dive. Kinda like a fuzz buster, what today would be called a threat receiver.

Answer 2

Sonar was actually invented in 1915 and perfected in 1918. All countries knew of and had sonars in WW2. U-Boats used sonar in the passive listening mode to listen for the very noisy engines of a convoy of ships to locate targets then use the periscope to aim thier torpedos. Subs navigated by use of compasses and when on the surface using the sun and stars. Subs in WW2 spent most of there time on the surface as running underwater was very slow going and hard on the equipment.

Answer 3

They navigated by compas, gyroscope, and by knowing how fast they have travelled, in what direction, and for how long, etc. (i.e. good record keeping).

They found ships by patolling. They might also see debris (garbage thrown overboard, and look at the currents and surmise where the ship that dump it may be now. Also, aircraft patrolled from the french coast, and when they saw something they radioed it in.

With the exception of about 6 months (when the naval version of the Enigma encoding machine got a 4th wheel) in 1942, the allies were able to break the German codes, and it the U-boats radioed in their position, they knew the general area to search for them in, and what areas to have cargo ships avoid.

Answer 4

1) U-boats wuring WWII found their targets by sighting them directly with periscopes, or by getting convoy positions relayed to them by the German scout planes.

2) U-boats, back then, navigated the old fashioned way - by DR (dead reckoning) and if the WX was good they would surface during sunrise/sunset to shoot stars and use celestial navigation.

I recommend you watch the movie DAS BOOT, about the life aboard a German Uboat during WWII. Very good movie, makes you feel like you are onboard and can smell the stench.

Hope this helps!