Some of the details from the original game have gotten a bit fuzzy over the passage of time.
But I think part of the plot of the game was that Carlson had failed on an assignment to Titanic but had gotten off safely and his employment with the government was being terminated because of his failure.
But going back in time gives him a second chance to save himself.
It is sort of a scavenger hunt .
You have to navigate Titanic and get items on a list.
One item is a painting by Adolf Hitler.
If you retrieve it successfully , Hitler becomes a successful artist, but never a dictator.
If you get everything on a list , you ''win'' the game , prevent WWII and a lot of other bad things from happening , Carlson retires with honors and man goes to the moon in the 1940's.
Toward the end of the game you are in real time and racing against the clock to get everything and get off safely.
If you get nothing , nothing changes , WWI and WWII happen, the Russian revolution happens, et cetera , et cetera, and so forth.
But if you get some but not all on the list, even worse things happen , Germany wins WWII for example.