Trying to build a Core rule with 1941 basic map and expanding with further game.
Here is what I get.
I voluntarily not use the Japan SZ, because I don’t think it is relevant to place Convoy in IC’s SZ.
I would prefer to use SZ which also have an Islands Group in it (to more easily add the option of neutralizing Convoy by controlling Islands. SEE EDIT below.)
Interesting SZs (IMO) for Convoys 1941 /1942.2/ AA50 /G40
JAPAN (1941 Japan SZ 45) (1942.2 Japan SZ 60 & SZ 62) (AA50 Japan SZ 62) (G40 Japan SZ 6)
1941
SZ 46 (Coastal China SZ, Formosa on map SZ but not a TT)
SZ 38 (Philippine Islands and Caroline Islands SZ)
SZ 31 (Malaya SZ, no Island in SZ)
1942.2
SZ 61 (Coastal China SZ,Formosa 0 IPC TT on map SZ)
SZ 48 (Philippine Islands SZ)
SZ 50 (Caroline Islands SZ)
SZ 36 (Malaya SZ, no Island in SZ)
AA50
SZ 61 (Coastal China SZ,Formosa 1 IPC TT SZ)
SZ 60 (Okinawa SZ 1 IPC TT)
SZ 50 (Philippine Islands SZ, US original TT)
SZ 51 (Caroline Islands SZ)
SZ 36 (French Indo-China Thailand Eastern SZ, Hainan Island on map but not a TT)
1940 Global
SZ 20 (Coastal China SZ, Formosa 1 IPC TT on map SZ)
SZ 35 (Philippine Islands SZ)
SZ 34 (Palau Island SZ)
SZ 33 (Caroline Islands SZ)
SZ 36 (Hainan Island 0 IPC TT)
SZ 37 (Malaya SZ, no Island in SZ) But it is a UK TT on initial set-up.
PACIFIC RUSSIA (1941 SZ 47 : Soviet Far East and Siberia / SZ 45, Siberia shared with Japan)
(1942.2 & AA50 SZ 62, Buryatia SSR shared with Japan)
1941
SZ 43 (Midway SZ)
SZ 47 (Coastal SZ of both Soviet Far East and Siberia)
SZ 48 (Alaska SZ)
1942.2
SZ 57 (Midway SZ)
SZ 63 (Coastal SZ of both Soviet Far East and Buryatia S.S.R.)
SZ 64 (Alaska SZ)
AA50
SZ 57 (Midway SZ)
SZ 63 (Coastal SZ of both Soviet Far East and Buryatia S.S.R.)
SZ 64 (Alaska SZ, Bering Strait SZ)
1940 Global
SZ 25 (Midway SZ) Much lower on the south
SZ 8 (Aleutian Islands SZ) More on the way toward Russian Coastal TTs.
SZ 2 (Alaska SZ)
SZ 3 & SZ 4 (Coastal Soviet Far East)
SZ 5 (Amur, Siberia and Soviet Far East SZ)
UNITED KINGDOM
1941 (INDIA ICs SZ 29 & AUSTRALIA ICs SZ 33 )
SZ 27 (French Madagascar SZ)
SZ 28 (Middle East, Italian East Africa & Anglo-Egypt Sudan SZ)
SZ 29 (India SZ)
SZ 33 (Australia SZ)
SZ 37 (New Guinea & Solomon Islands SZ)
1942.2
(INDIA ICs SZ 35 & AUSTRALIA SZ 38, SZ 39, SZ 45 & SZ 46 )
SZ 28 (French Madagascar, near Union of South Africa SZ)
SZ 34 (Persia, Trans-Jordan, Egypt, Italian East Africa & Anglo-Egypt Sudan SZ)
SZ 35 (India SZ)
SZ 48 (New Guinea SZ) [A less interesting choice for Convoy SZ, since it is less in line with US shipping line.]
SZ 49 (Solomon Islands SZ) [OOB Japanese occupied TT]
AA50
(INDIA ICs SZ 35 & AUSTRALIA SZ 39, SZ 40, SZ 41 & SZ 47 )
SZ 28 (French Madagascar, near Union of South Africa SZ)
SZ 34 (Persia, Trans-Jordan, Egypt, Italian East Africa & Anglo-Egypt Sudan SZ)
SZ 35 (India SZ)
SZ 48 (New Guinea SZ) [A less interesting choice for Convoy SZ, since it is less in line with US shipping line.]
SZ 46 (Solomon Islands SZ) [OOB UK TT]
1940 Global
SZ 72 (French Madagascar SZ)
SZ 71 (Union of South Africa SZ)
SZ 76 (Italian Somaliland, Ethiopia & British Somaliland SZ)
SZ 79 (Western India SZ)
SZ 80 (Eastern Persia, Persia, Irak & Saudi Arabia SZ) [OOB Australian Convoy SZ]
SZ 39 (India SZ with Ceylon Island)
SZ 37 (Malaya SZ)
AUSTRALIA (SZ 54, 55, 56 , 61 and 62)
1940 Global
SZ 46 (New Guinea SZ) [Not an australian Convoy SZ but an Australian TT]
SZ 49 (Solomon Islands SZ) [Not an australian Convoy SZ but an Australian TT]
SZ 53 (New Hebrides SZ) [Not an australian Convoy SZ but an French TT]
SZ 54 (Queensland SZ) [OOB Australian Convoy SZ]
SZ 62 (Sydney, Victoria SZ) [OOB Australian Convoy SZ]
SZ 63 (New Zealand SZ) [OOB Australian Convoy SZ]
UNITED STATES of AMERICA
West Coast (1941 SZ 42) (1942.2 & AA50 SZ 56) (1940 Global SZ 10)
1941
SZ 39 (Wake Island SZ) [OOB US TT]
SZ 40 (Hawaiian Islands SZ)
1942.2
SZ 52 (Wake Island SZ) [OOB JAPANESE TT]
SZ 53 (Hawaiian Islands SZ)
AA50
SZ 52 (Wake Island SZ, 0 IPC TT)
SZ 53 (Hawaiian Islands SZ, 1 IPC TT)
1940 Global
SZ 31 (Wake Island SZ) [OOB US TT]
SZ 26 (Hawaiian Islands SZ) [OOB USA Convoy SZ]
SZ 25 (Midway SZ) [This island location is not interesting for plausible Russian Convoy lines.]
SZ 30 (Johnston Island SZ) [OOB US TT] [Could be a USA Convoy SZ since it is a direct line of travel from Australia.]
Looking up for USA Pacific Convoy SZ for 1941, 1942.2, AA50 and G40,
I think Hawaiian SZ (a US TT on all 4 maps) could be preferred over Wake Island because in 1942.2 it is controlled by Japan.
Unless we want to play optional Convoy neutralized by Island Controlled of SZ 52, so in 1942.2,
US Convoy in Wake SZ 52 could be neutralized by Japan until it is liberated, it would be a similar scenario to Solomon Islands SZ 49 which would be under Japanese control but can have a UK Convoy in this SZ 49.
This would create a bigger incentive to go Pacific for US and to conquer both Islands, so to relieve Convoy under Japanese grasp.
EDIT: If Islands group are treated as Subs or BBs and, on enemy’s player combat phase, can be used to flip downside all NCMs in SZ, then it can be possible to let NCMs in SZ 52 and SZ 49 face up in the 1942.2 set-up.
Japanese players would have to declare Convoy Disruption via Island Base on his turn.
This make Wake Island an interesting SZ to put Convoy in it, and would provide a game motive for Japanese player to do the same as Japan did in december 1941.