I hadn't seen this on the sub-reddit and thought it might be helpful. I did the frontline quiz until I got all the answers. The code only gives you 5 battles in the tank as a rental and only one code can be activated per account so chose wisely.
The tanks are: *tank name – code*
- M 41 90mm – IAMM4190202
- 50 TP – IAM50TP
- T26E5 – IAMT26E52020
- Lowe – IAMLOWE2020
- Progetto – IAMPROGETTO2020
- LT432 – IAMLT4322020
- Skorpion G – IAMSKORPION2020
- Strv S1 – IAMSTRVS12020
- ELC Even 90 – IAMELCEVEN2020
- T29 LT – IAMT92LT2020
- Somua SM – IAMSOMUA2020
- AMX M4 mle. 49 – IAMM4492020
- TS-5 – IAMTS52020
- Kanonenjagdpanzer 105 – IAMKJP1052020
- Mauerbrecher – IAMMAUERBRECHER2020
- Turtle MK.1 – IAMTURTLE2020
Source: https://www.reddit.com/r/WorldofTanks/comments/g9mlzv/frontline_test_tank_codes/