Marshall Islands 1941: no ships...

In TMOwTw I was sent to the Marshall Islands in 1941 to patrol there. I was there on December 9 and patrolled there until December 22.
I've been shelled a few times from an island but haven't seen a single ship. I'm half way through my fuel oil and I'm about to get back to Hawaii now. Is this normal? During my patrol I changed course many times. Should I? Or should I have made my route exactly at the start of the mission so that the game could have presented an opponent somewhere along that route? I don't know... Can someone explain to me what's going on here?

Edit: And, off course, I saved my game many times...

[propbeanie]

That was rather common for the US subs, especially early in the war. There was not yet much inter-island traffic in the area yet. The orders given the boats doing their first war patrols in the Marshalls were such that the US brass expected the subs to find a lot of targets in the area, believing at the time that the Pearl Harbor attack had originated from there. But the US also knew little of the Madates and their military status, so the submarines were also ordered to recon the areas they patrolled, by getting in close to the reefs and seeing if they could spot shore installations and air fields, while also documenting tidal and weather info. Doing those chores, they also discovered that the USN charts of the area were woefully inadequate, so they started that documentation process also... There was a LOT of blind groping early in the war, and the US did not understand how to use their submarines properly.