Ok, I've done a bit of searching and finnaly found this page :
http://www.locationworks.com/sunrise/2040.html#40
Just as I thought, you don't need to already know your Latitude to find your Longitude, just look through your periscope as the sun sets and rises and mark the bearing. Add that to your sub course to get the Azimuth of the sun. Find the closest matching day in the table and you'll at least know if you're at 40, 50, or 60 etc degrees of Latitude and then continue with your calculation to find your Longitude. I've seen it work in both SH3 and SH4(altough you need to adjust the base time to gmt). So no need for the sextant, but that leaves you with a vertical line of 600nm, while a good sextant would drop that value to 6 miles. So here's a few things that would make this navigation bit a really interesting choice for the realism buffs whithout being to overwhelming. Who knows, maybe they want to implement such a think in SH5. You'd just enable these from the dificulty menu with the option "Real Navigation"

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1. a true sextant with subdivisions scale (Vernier scale). it's just a Periscope view with a buffed up dual lens stadimeter

2. a hideable Lat/Long markings layer on the map, should be much better that the one in SH4 or at least explain how to get the minutes (60 miles in a degree, I know).
3. the ability to turn off all map markings for the sub, including a simpler course plotter that is neither glued to the sub, nor does it update the distances to waypoints while the sub moves. The line tool is not cut out for this.
4. better map marks, that let us edit the label on multiple lines (description, time: "hans' feet stink/18:47")
5. 1x time for game and message box with the message "Nav point reached" if you want to make those course changes manually.
6. clocks in game for GMT and Base time and maybe a large scale chronometer that you can reset whenever you want, great for manually timing those checkpoints.
7. a good values table similar to the one from the above link, that uses the actual game mechanism for the motion of the sky.
8. a drop down white map for the actual attack plotting. So that we don't clutter the navigation map to much. What I actually do in the game is go to the middle of the pacific and plot my attack there at a much greater scale to get rid of the line value issue.
and of course
9: the ability to automate all of this for the kaleuns who hate gps precission but don't want to waste time calculating. The Navigator Officer should have the following options:
-"Estimate current position along course" , which would simply place a mark on the map along the plotted course, simulating dead-reckoning.
-"Get Lat/Long Position" when the weather allows it, which would place a circle with an estimated true position and a label with the time (the diameter of which would depend on the navigator's experience).
-an "Autoupdate positions at sunrise/zenith/sunset" checkbox
-and a "Experience determines the time it takes to make the above calculations" option in the Menu.
During cruising mode, the navigator should be able to automatically adjust the course at each real position calculation. I should point out that any departures from normal cruising should brake the Navigator's routine and put him in a "behind the scenes continually try to plot course changes during attack and destroyer ping-pong" so that you don't get helplessly lost after a 6 hour attack procedure. Here, a "return to course" command would work just as it does know but it would introduce a considerable(but acceptable) ammount of deviation.
Phew finished

. If you think this post was long, wait for my "SH5 Interior Interactivity" thread

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