A good article of german WWII torpedoes
http://www.navweaps.com/Weapons/WTGER_WWII.htm
i) I don't think that was possible in RL.
ii) I don't know
iii) Taking into account a warhead of 300 kg of explosives an arming range less than 300 m would be just fatal to the Uboat.
The blast of the torpedo was able to brake 3000 - 4000 tons ships ,imagine the results on a 700 tons U boot.