Heh, okay, quick explanation.
In the Red Baron world, SP means Single Play. This is when you play against the computer AI and fly the campaigns.
MMP means Massive Multi Player. This is the on-line portion of the sim, where players can fight against one another.
In SP, you fly according to the squadron to which you belong. Squadrons can be assigned to four maps: Alsace, Flanders, Marne, Verdun. The four of them together overlap and represent the entire Western Front. The Flanders map does have water on it, in the far north. The trenchlines unfortunately end before they get to the water, so the ocean is only on the Allied side. However, it is there.
On the MMP side, players have a choice of five maps. In addition to the four named above, you also have what's called the Island Map. I found a picture of it, on the RAC webpage describing an MMP war scenario. It's here:
http://www.citigraph.com/rac/LovelyWar1.htm
As you can see, this is an island surrounded by water. Because the island map is small, the action is close. On-line pilots use this when they don't want to take a lot of time flying to meet an enemy.
So, to summarize, in Red Baron, there are two places where you will encounter the ocean. One is on the Flanders map. The second is on the island map. You can see the Flanders map in both SP and MMP. The island map, however, is MMP only. It does not exist in the SP campaign.
Does that help?
John