Sub control question

[kapitan z.s.]

I dont have the button on my left side of the screen that you drew a red arrow to. I cant seem to order to a specific depth, i can ask it to dive. Im alittle confused. Also I have hit several cargo ships with 2 torpedeos and the damage bar is barley under half way, is there a tip to drop a small to med sized cargo ship with two bullets, im tired of using my deck gun all the time. Thanks