Upgrading CAGs

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Running HOI2 v1.3a
According to the Wiki, CAGs are automatically upgraded when CVs are in port after upgraded Escort Fighters have been researched. Yet CAGs are available for purchase in the brigade section, surely this is not required.
I also note that the UK has CAG3 (Swordfish & Sea Gladiator) as a starting point in 1936 and I've never had an upgrade (although I don't think I've played past 1942 and having Mosquito Vb as the escort fighter[(lvl 2?]), CAG3 would seem to be a high starting point.
When do the upgraded CAGs start appearing?

 

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Running HOI2 v1.3a
According to the Wiki, CAGs are automatically upgraded when CVs are in port after upgraded Escort Fighters have been researched. Yet CAGs are available for purchase in the brigade section, surely this is not required.
I also note that the UK has CAG3 (Swordfish & Sea Gladiator) as a starting point in 1936 and I've never had an upgrade (although I don't think I've played past 1942 and having Mosquito Vb as the escort fighter[(lvl 2?]), CAG3 would seem to be a high starting point.
When do the upgraded CAGs start appearing?

CAG levels appear with the relevant Carrier Research Level, not Escort Fighters.
Hence UK has level 3 carriers (Ark Royal Class), none deployed, as the highest available at the start of 1936 they then have CAG 3 for purchase.
To upgrade the CAG higher than level 3 you need to research Carrier Level 4.
Note from memory the UK carriers at the start of 1936 have CAG 1 & 2 deployed so they will need to be upgraded in port, even though the Carrier class is either 1 or 2.

 

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Thanks.
All became clear last night when I played the US and researched a new carrier.
You're right about the UK starting level. The level 3 CAGs are in the Upgrade queue at the start of the 1936 game.