Battlefield 1942: Secrets of WWII is the second expansion to Battlefield 1942. The expansion features weapons, gadgets and vehicles based on research and prototypes that were made during World War II. It also introduces eight new maps, six of which are objective based. In the objective based mode the allied must destroy or sabotage axis constructs. The axis engineer can repair the construct if they are not destroyed, meaning the allied attacks must be swift. The allied will lose tickets as long as the targets are still standing. The axis will start to lose tickets when targets are destroyed.
None of the weapons and vehicles are playable on the old maps.
None of the maps are based on historical battles, which they were in the original game. Nonetheless, the battles are given a timeframe.
- Kbely Airfield (August 1943): Outside of Prague, the allied forces must infiltrate an airfield and destroy the UFO-like prototypes that are being constructed there.
- Telemark (November 1943): The Germans are producing heavy water to construct atomic bombs. The allied must destroy the generators in the factory.
- Mimoyecques (July 1944): The Germans are constructing a large cannon capable of launching rockets at London. The allied must destroy the cannon by throwing explosives down the ventilation shafts.
- The Gothic Line (September 1944): A regular conquest based map.
- Hellendoorn – The Netherlands (Mars 1945): The allied must destroy the V2 rockets within a German base.
- Essen (Mars 1945): Allied forces must infiltrate a weapons factory and blow up the fuel depots.
- The Eagle’s Nest (April 1945): Inside the Eagles Nest (Hitler’s Cabin) there is a safe containing secret information. The allied forces must destroy this safe
- Peenemüende (May 1945): A regular conquest based map.
- Remington Auto 5-Shotgun: A semi-automatic shotgun. An excellent close range weapon.
- Mauser K98-grenadelauncher: A regular K98 rifle equipped with a grenade launcher. Good at dealing with machine gun nests.
- Throwing Knife: A deadly throwing knife available to both sides.
- Light Bren-Machine Gun: A Light and versatile machine gun that is effective against infantry and airplanes.
- Gewehr 43: A semi-automatic sniper rifle.
- Silenced Sten Mk2: A stealthy and capable sub-machine gun.
- Fallschirmjager Gewehr 42: A versatile rifle for German paratroopers.
- Guided Wasserfall-Missile: Players can take control of the missile by entering a silo. The missile is very fast and only has a small amount of fuel, but will kill anything it hits.
- Rocket Pack: Does what jetpacks do best. While wearing the rocket pack the player can only use the same weapons as the German medic. It has a limited hover ability, so the player must be careful not fall to their death.
- McDonnel F-85 Goblin: A very small and fast jet plane capable of quick hit and run attacks with its machine gun.
- Natter Rocket Aircraft: Handles very much like the Goblin, with the exception that it is launched like a rocket. This means it is incapable of landing. Luckily, it comes with a parachute. It is equipped with unguided rockets.
- Horton HO 229: A fast jet plane with unguided rockets and machine guns.
- Armstrong Whitworth AW-52: Very much the allied version of the Horton, except it is armed with bombs instead of machine guns.
- XA/42 with Machine Gun-Mounted Sidecar: A two person motorcycle armed with a machine gun.
- R-75 with Machine Gun-Mounted Sidecar: The German equivalent of XA/42.
- LVT4 Water Buffalo: An amphibious APC capable of transporting troops across land and sea. It is armed with two machine guns.
- C-47 Cargo Aircraft: A large aircraft that works as a mobile spawn point for the allies.
- Sherman Tank with T-34 Calliope: A Sherman Tank with T-34 rocket launcher. Capable of defeating vehicles on long distance.
- Flakpanzer: A Panzer IV armed with 37 mm machine guns. It is very effective against airplanes, infantry and light vehicles.
- T95/T28 Super Heavy Tank with AA Gun: A heavily armored tank that can withstand heavy damage. It is armed with a machine gun and is very capable of dealing with infantry.
- Sturmtiger: A modified Tiger tank that deals heavy damage. The downside is that it has limited ammo.
- Commando Raft: A small raft armed with a machine gun. Capable of transporting troops across water fairly quickly.
- Schwimmwagen: An amphibious jeep armed with a machine gun.