I don\'t think anyone answered your specific questions.

-A U-boat used primarily the eyes (with binoculars) of the lookouts - four usually, each watching a specific 90 degree quadrant. In clear weather during the day they could spot a plane miles away and get under in plenty of time - if they were on their toes. If the weather was bad and the plane was radar equipped, chances are that the plane would pop out of the mist and clobber them before they could do anything. At night they would be able to see precious little - and be liable to surprise. Remember that the boats engines usually drowned out the noise of an approaching airplane.

Radar detectors and some radars were used, but these had varying degrees of effectiveness. A boat would dive if the radar detector indicated someone was getting close - same as a lookout spotting a plane.

-A well trained VIIC could go from surface running on diesels to fully submerged at periscope depth in a bit over 30 seconds- maybe 35 - 40 secons being a bit long. A lot depended on the crew\'s training.

-The usual tactic when attacked from the air was to get under as fast as possible, and dive deep as quickly as possible. A sudden turn after submerging to throw off a depth charge drop was common. Given enough warning this was very effective against depth charges, but not against the Fido acoustic homing torpedo. If you were slow in getting under or got surprised at or near the surface the shallow depth charges dropped on you would be lethal.

At one point in the war Doenitz ordered U-boats to stay on the surface and \'fight it out\' with added AA armamament. Losses were horrid - it was an insanely stupid order.

-\'The Swamp\'? new one on me.