I decided to post a quick progress report because this update is taking so long. Here are a couple of the features I've added this week:
- The arctic ice sheet is now simulated - you can sail under it and even break through it if you have enough speed. Trying to smash your way to the North Pole like some kind of weaponized icebreaker is a definitely a bad idea though.
- The AI for ships, aircraft and convoys have all been significantly improved. Nations will react faster and more aggressively towards any hostile subs detected in their waters, especially if you start launching torpedoes or missiles. Ships will now radio your position to each other and call for air support if it is available. Pilots are also better at planning attack vectors and flight paths.
- Cities can be destroyed by nuclear weapons (meaning you are unable to refit there) and nuclear blasts will irradiate the surface (making it unsafe to refresh your sub's air supply). It seems I've made a simulation of Nevil Shute's On The Beach

Before I release V0.25, there are still several tweaks and improvements to be made to the diplomacy code, the UI, and several of the onboard systems. I think all of the major features are finished though, so with any luck it should be out next week.