In case anyone is interested, I’ve also been working on some naval supply rules and like Narvik I settled on a naval movement/combat radius of 2 or 3 sea zones from friendly naval bases. Submarines and transports get a range of 5, since they operated at slower speeds which provided better endurance and range.
To go along with that I also am working on rules for oilers that would extend the range of naval units; right now I’m thinking that each oiler gives an additional 1-2 range. This would allow you to combine one or more oilers and a naval base into a long supply chain to your fleet, like the US and UK did in the Pacific. This also allows for interesting side-rules like German secret raiders who can act as oilers to supply the commerce raiding warships, or submarine oilers (the “Milchcow”).
If a fleet is suddenly rendered out of supply, either due to loss of oilers or naval bases, I say that they are not allowed to initiate combat, must retreat immediately if attacked (not sure yet if I’m happy with this), and must non-combat move towards the nearest friendly naval base on their turn until they are back in supply.
I have not yet been able to test any of these rules to verify they are fair and fun, but it seems like they should generally work.
Most WWII-era ships had a designed range of about 10,000 nmi at 10 to 15 knots (typical cruising speed). Bumping up to combat speed drastically reduced that range, down to about 2,500 nmi. I’ve done lots of calculations and in Global War 1936 each sea zone on the map is about 1000 nmi wide, so reducing the combat radius of ships to 2-3 sea zones from a naval base is actually fairly accurate if you assume a fleet at sea is doing a mix of cruising speed and combat speed and either being supplied by a local oiler at the naval base, or maybe the fleet is running back and forth between port and their assigned sea zone each turn. Then each oiler unit would represent a collection of oilers and supply ships able to carry supplies further out to sea.
