How far you launch torpedos when they miss? You need to be close enough and aim at the ship that is moving in one direction, in Midway mission all ships are scrambling around, turning, slowing down, accelerating and so on so it may not be the easiest possible mission for beginners, even if it's fun because when there is that amount of steel in the sea you almost always hit something
Also, if you are afraid about detection, when first torpedo hits there is no coming back after last ship sinks so take the truth that they know where you are easily, even if they know your position they can't always get there. And if they can dodge your torpedos, you can dodge their huge ships
Good luck and happy hunting!
(and yea, you aren't only one who couldn't hit a wall with torpedos at the beginning

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Elektroniikka-Asentaja = Electronics Assembler. In finnish, Just in case someone wants to know..
New rig for noisy running:
Desktop w/ Asus P5QC motherboard, Intel Core 2 Duo 2,94 GHz processor, ATI Radeon HD 4800 series graphics, 4 GB DDR3 Ram and 1297 GB hard drive memory
There is a good possibility that the above post was written with a phone so please forgive the typos