Hi there, I had this same problem on my older PC, the game was very laggy and used up a crazy amount of resources, even though my CPU was good the game was barely playable.

I have fixed the problem by setting these compatibility settings:
 (right-click->settings->compatibility)
Win98/ME Compatibility Mode
Run as admin
Disable Visual Themes
Disable Desktop Composition

You will probably need to apply the changes to all exe files NF uses, which are:
C:\Program Files\SD EnterNET\NavyFIELD\NavyFIELD Launcher
C:\Program Files\SD EnterNET\NavyFIELD\NavyFIELD
C:\Program Files\SD EnterNET\ENFUNS Updater\ENFUNSUpdater

After I changed this, the game suddenly played smooth with no problems both in shipyard and in battles.

You can also try a different mode other than Win98/ME, but for me it was the only option that fixed the issue - neither higher nor lower worked for me personally.

Hope this helps,
pet

Thank you very much for your detailed reply ,very helpful indeed. I managed to get the game running with no lag in shipyard and in game. Using windows NT 4.0(service pack 5) for my compatibility mode,my system uses window 7 !! Only problem now is that game hangs and crashes at the result screen when I press the next button. at least now I can enjoy the game but am unable to level up ;-) Edit . It does appear as though sailors are gaining experience even with the crash. Just have to restart game after every battle :-(