[el_Salmon]

I'm a newbie in submarine simulators, sorry. I'm reading Sub Command Official Manual and Bluebook 20 (Spanish). I've found this post with the same problem:
http://207.44.164.159/phpBB/viewtopic.php?t=26465

I don't know how to use the High-Frequency Sonar of 688(i) to round up icebergs and ice walls.

[Nexus7]

Firs u usually can look forward and upwards in the HF. To recognize obstacles in normal behavior look forward...
When you see objects in the HF just click on them and click MARK. Go to navigation map and you'll see the exact position of the iceberg, mine, satellite or whatever.

[MaHuJa]

The HF sonar on the 688(i) is located on the ship control screen. Once you turn the switch to its on position, the background of the display itself should darken, with light areas representing objects and misc. effects (ship wakes). Clicking the screen itself should add a marker to the nav screen at the position of each object visible on that screen. (Note that the objects are bigger than the cross, when you zoom in)

[el_Salmon]

Thank you!

HF Sonar it's like a pseudo-3D vision in short range.

[Nexus7]

Thanks for correcting Mahuja.
The MARCK button is for the Seawolf not for the 688i