The amphibious craft "New Orleans" is a small ship, with no submarine tracking capabilities. It depends on its escorts for submarine awareness and defense. The sub was running at high speed at periscope depth, which puts the "sail" area just below the surface of the water.
Actually, collisions happen all the time. A collision is not necessarily a career-ender. A grounding almost always is.
About 30 years ago, one of our cruisers collided almost head-on with a smaller ship, a destroyer or cruiser in night maneuvers. Investigation showed that someone misread the radar on the smaller vessel, and the overabundance of lights on the carrier made it very difficult to determine which direction it was going. The cruiser thought it was following the carrier.
The collision took almost all the superstructure off the cruiser, killing a goodly number of sailors. I learned a lot about it talking to one of the officers who manned the information phone line at command in the hours after the collision, answering calls from worried relatives.