Still not confirmed as of yet, but for those who want to design a lengthy 'tube' type or just generally huge submarine designs. Certain generated caverns only permit a certain amount of horizontal space in sections where you must travel downward such as most starting points of Barotrauma's areas. If you use a 'topwall heavy' piece in the editor you can stretch it across above your submarine design to measure how many pieces long in total it is. The 3 vanilla sub designs are 9-10 pieces long in total, but far as I've seen anything longer than 16-20+ will have trouble in certain levels, most cases with the auto-pilot.

Here are some tips:

*Give your submarine a shuttle engine in case if main engine having to break, so it would drive submarine at slower speed, but otherwise without mechanic it would be stuck forever, unless pushed by monsters.

*Give it so many batteries there would be no malfunction in grid load upon leaving entire submarine's power to batteries, that's how you spend empty space.

*Have a basic diving equipment for one person or maybe more in command.

*Replace connection panel accesses "Screwdriver" with "locked" in submarine editor, so griefers won't unwire them. Doing so would probably in the lore of you submarine cost a lot of credits to secure your submarine like it. It would make sense, if submarine was small and it's creator was somebody wealthy.

Submarine having all those things: