atari2600land has kept on developing the second part of GoSub and released another early preview.

Release notes:

I added being able to shoot the enemies. But what I need help with now is the mini-game. I’m thinking Combat for this time, and I need your people’s opinion on one thing: When the sub hits the wall in the minigame, should it A.) keep ramming the wall; or B.) bounce off and go in the opposite direction? version 18b has the first option and version 18c has the second one. Many thanks to Mike Rideout for helping me with this part. To get to the mini-game, at the title screen, press the select switch until the first digit gets to 2, then press the reset switch.

http://www.atariage.com/forums/index.php?showtopic=111937