Assault Gun Unit upgrade.
 

In the past, whenever I played long campaigns, I always used a lot of infantry units. I usually bought for my core units what was best to use in the game without a lot of concern for historical accuracy in the unit mixes. Now I want to try the campaigns with a more historically accurate unit mix.
When I purchase my 1939 infantry formations will any units be able to be upgraded to assault gun vehicles in later years? If I remember correctly you can only upgrade AFVS to AFVS, and not for example, infantry gun units to assault gun units. I know I can always buy assault guns as new units for my core when they become available, but I was hoping to be able to upgrade an experienced unit which I started in my 1939 core. I don't remember any assault guns being available in 1939. My new game will arrive in a few days so I am trying to refresh my memory on this.
Thanks for any info.

Re: Assault Gun Unit upgrade.
 

Towed artillery (or mortars) -> Artillery (including SPA). That one would be best if you want to use units with a high artillery skill and hence faster indirect request response times as Sig or Hummel later.

If you just need AFV (as SP-AT) then you may want to convert something that was originally an ATG. So upgrade your 37mm ATG or flak.

As Germans, I like a few of those really cheap armoured cars with just an MG, a pair supporting each rifle company for anti-infantry work in Poland and France. These are never risked as recce, so the survivors can often have higher skill. They are good for hosing down enemy rifle sections and can zip back to the ammo carriers in the rear echelon fast for a reload if required. They often become stugs or marders, come Russia.

Cheers
Andy