[Heibges]

The S.O.P for a patrol would be to stay on the surface and conserve as much fuel as possible. Soundchecks were conducted at dawn and dusk, so the uboat wouldn't be surprised in the rapidly changing visibility conditions.

I heavy fog, and conditions of extremely poor visibility, uboats stayed submerged because the danger of being rammed was greatly iincreased.

Airborne radar caused the the uboats to have to recharge batteries at night and attack submerged during the day. Their great successes had been mostly based on the highly mobile nighttime surface attack.

After Black May, uboats were increasingly forced to stay submerged for up to and including the entire patrol. This was accomplished through use of the snorkel. Due to its low underwater speed, the only way a uboat could intercept a target now, was if it steamed right over it. Also, by this time, uboats spent much more of their time going to and from port rather than patrolling for the same reason.

During the good years, to intercept a convoy they would set up a patrol line in the convoys path. They would move toward the convoy at low speed. If they got to a point where they should have intecepted the convoy, but hadn't, they turn around and follow a reverse course at hight speed, then start the process again. The first uboat to spot the convoy became the contact holder and would broadcast updates every hour. If a contact holder stopped broadcasting, another boat was expected to take over as contact holder. Keep in mind, uboats did not conduct "coordinated attacks" on convoys in the tradional military sense in the word.