What do you have to do to unlock the secret achevements on call of duty 3 on the xbox 360?

Answer 1

Well i dont have the game but i do have a very useful cheats book that i havent yet used. My book does'nt say secret acheivements, just states acheivements. Well anyhow:
1) for A War Hero (30): capture the final objective in war mode. Must be ranked match (multiplayer)
2) Allergic to bullets (25):avoid getting hit more than 30 times during a mission.
3) American Infantaryman (20):complete a mission as an American type soldier.
4) Assault trooper (15):complete a mission by firing only assault rifles. Melee attacks dont count.
5) Basic training (5): complete the basic training in the begining of Saint Lo.
6)battlefield Scavenger (15):complete a mission by only firing german weapons. Melee attacks don't count.
7)Big air (25): find a big jump and catch some air
8) british commando (20):complete 2 missions as a british type soldier.
9)canadian highlander (10): complete 2 missions as a canadian type soldier.
10) Captain (40): Receive 2000 total points in ranked matches ~(multiplayer)
11) close quarter combatant (100): complete a mission without firing a round. Player can make use of Melee attacks and hand grenades.
12) Colonel (80): receive 20000 total points in ranked matches (multiplayer)
13) Conservationist (20) : complete mission using less than 300 rounds of ammunition.
14) Doc (30): Receive ten of your teammates in ranked match getting a teamkill ( multiplayer)
15)EXTREME (25): found a big jump and caught some air.
16)General (120): Receive 40000 total points in ranked matches (multiplayer)
17) Grizzled Veteran (150): complete the single player Campaign on Veteran difficulty.
18) Hot Potato (25): Pick up and return five live grenades.
19)Lieutenant (20): receive 200 total points in ranked matches (multiplayer)
20)Major (60): receive 8000 total points in ranked matches (multiplayer)
21)Polish tanker (15): complete two missions as a Polish type soldier.
22)Purple Heart (5): rewarded for perserverence despite grevious injuries.
23) Rifleman (15): Complete a mission by firing only bolt action rifles. Melee attacks don't count.
24)Still Ticking (30): complete a mission without dying or using check points.
25) Supply Officer (15): supply ammunition to at least 20 friendly soldiers in a singal ranked match (multiplayer)
26)Victory Medal (30): be the player with the highest score and on the winning team in a ranked match (multiplayer)
27) Won the War (80): Complete the single player campaing on any difficulty setting

Thats all my book has on Call of Duty 3, not sure if thats the info you wanted though but hey i dont see any other answers here :), hope it helps anyway.

Answer 2

I have call of duty 3 and have only unlocked this one:
Big air 25g: i think it is the third mission in the game. A british mission when you are in a jeep and you will come to a ramp, go over that in the jeep and you will get the 25g.