1. Individual block pressure limits and pressure damage to grids (ex. large ship full light armor block pressure limit: 2 km | large ship full heavy armor block limit: 6 km).

2. Variable pressure limits based on gravity of planet, with 1g being standard settings (planets with lower gravity allow you to go deeper than you could on other planets)

3. No pressure damage done to player when in pressurized environments below 500 m.

4. Capability of drowning w/ oxygen time limit when helmet is open (maybe 15 to 30 seconds before the player starts taking damage).

5. Extra pressure damage done to blocks surrounding a vacuum (requires 1.)

6. Thicker layers of armor allow for deeper traversal (also requires 1.)

7. In-game option to choose whether or not guns stop functioning when underwater (Missile turrets always work)

8. Electrical components and blocks exposed to water damages them (basically just batteries and powercells)

9. Make warheads water-neutral (stays in place at any depth)

Feel free to post any ideas of your own!