How was a submarine less formal?

The main factor was that there wasn’t enough room for formality. On long patrols in the tropics, “uniforms” became much less uniform. In WW2 submarines, shaving generally wasn’t required. There were more informal conversations and banter. In quiet times, there would be verbal rehearsals for equipment failures or casualties. All of this was usually acceptable as long as everyone was also paying attention to their tasks and doing them well.

Another example was that “officers’ country” couldn’t be avoided as it could on a surface ship. There was only the one level that could be used to get through the boat. The crew had work to do or meals to eat that required passing through the officers’ and chiefs’ berthing in the forward battery.

However, being less formal did not mean that the officers or crew were disrespectful or less precise when doing their jobs.