Visual range
 

Today i found my first juicy prey. A large modern tanker. The weather was perfect. What is the visual range of detection for a surfaced sub ? I mean how close could i get without being detected ?

It depends on the weather. Seas as smooth as glass during the daytime you can be detected before reaching torpedo range if the prey has a well trained watch crew. I can't remember the exact numbers but you should go to periscope depth about 6000 yds from the target. I can usually get in to 5000 yds in the daytime before I pull the plug, but I try to stalk and attack at night so I can get nice and close.

It also depends on what mods you may be running. In TMO you can get detected very far away. Recently I was detected at 6500 by a DD on a moonless night in high seas. That's why I no longer use TMO. I love the mod butmy preferred ride is a S-Boat & while TMO may make for a challenge for the Gato jockeys it's nearly suicide for a S-Boat skipper.

Yes, depends on the mod - stock detection distances are pretty far. RFB is probably the most generous, but even there I do not typically get within 1000 yards.

One tip: detection is affected by your speed, your boat's height and your aspect (that is, which way you're facing relative to the ship). If you go decks awash, reduce your speed to 5kt or less, and put the enemy ship as directly on your bow or stern as possible, you're least likely to get detected. Running at high speed with your entire side exposed will get you detected from long range even at night.