I will try to explain better i think the post is not clear. When you save a game you have the option to save a replay, you can quit and load the patrol, and save the replay again after that only if you have a save with replay already.
With this tweak you can go inside the sub in the replay, and order speed, the submarine will only reflect that in the visuals (the submarine will not obey), also you can see all stations inside the sub, and 2d parts (map, messages etc) and manipulate the scopes (radar, periscope, hydrophone).
I post this because i'm sure some captains would like to show their career adventures.