I couldn't interact with the shells, they aren't pushablr and e didn't do anything. The two straws are prompted with "e" but nothing happened. Does the ship need to be powered for that? All my coal gets stuck in corners constantly...
You need to grab them by holding "G". press C to see all the controls.. after you hold G to carry ammo / coal, you'll be able to drop it where it needs to go..
When you drop ammo on guns (straws), they will load up with a green indicator. Later on you will be able to press E to shoot.
Also, the submarine only moves when enough coal is loaded, so I suggest you load 2 or 3 first.. then try moving with "i, j, k, l" to avoid having to manually control the steering :D