The Fourtieth Day Initiative (FDI) is a private army ran by Jonah Wade, serving as one of the main antagonists of Army of Two: the 40th Day.
By Jonah's order, the 40th Day launched their attack on Shanghai by destroying various buildings and starting to execute and/or take civilians as hostages. They eventually encountered the tough mercenaries, Tyson Rios and Elliot Salem, and at first, attempted to subdue them but instead tried to kill them. Many of the soldiers within the group were killed by the mercenaries during the battle.
Salem and Rios soon attacked where Jonah was hiding. The two murdered those protecting Jonah and then had a choice to kill Jonah and each other. Either which choice, the 40th Day left Shanghai with many casualities during the conflict.
- Grunt: Standard soldiers with the rank of "Private". They barely have any armour and sometimes wear sunglasses. Their weapons are often weak and are the most common members of the army.
- Elite: Elite soldiers are the leaders of Grunts and have the rank of "Corporal." They have more armour and usually carry Shotguns.
- Shotgun Heavy: A armoured up man who is armed with the R870. His head is exposed which allows the player to kill him. He is first encountered at the Shanghai Streets.
- Gatling Superheavy: An extremely armoured soldier who carries the GAU-19. The only way to kill him is to shoot the Ammo Pack until it explodes. He is first encountered in Case of Fire.
- Grenadier Superheavy: An armoured up soldier who wields the Milkor MGL. The only way to kill him is to shoot three grenade packs on his hips. He is first encountered at the Zoo.
- Flame Superheavy: An armoured soldier who carries the Flamethrower. The only way to kill him is to shoot the Gas Tank on his back until it explodes. He is first encountered at the Hospital.
- TDI Vector
- HandK G36C
- Remington 870
- Riot Shield
- Flamethrower (Flame Superheavy)
- Gatling Gun (Gatling Superheavy)
- MK Grenade Launcher (Grenadier Superheavy)
- R870 (Shotgun Heavy)