Go to the history menu screen. Now go to August 6th, 1945 (the date Hiroshima took place). Click the flashing book. During the game you can use the following keys to perform the corresponding function:

Code - Result

W - Win mission
K - Kill all enemies
L - Lose mission
A - Max ammo

To enable Hell Cheat Mode, do same as above, but afterwards find and select August 9th, 1945 (Nagasaki) and click again on the now non-flashing book in lower right corner. Hotkeys remains the same.