The following are the locations of the dog tags in order of when you find them:
#5 Corporal Ross Dixon. Once the dust clears from the train wreck in the train area, go through the hole the train made. On the platform to the right, between two metal boxes, is the dog tag.
#4 Corporal Arthur McDonnel. In the Command Center (where you use the 51204791 code in the computer) reach the side where the computer is located. If in the box, the dog tag is to the left of the computer, outside. Go to the outside corner of the box, where you can look over the electric stream. The dog tag is next to the box. You should see it shining.
#1 Private First Class Hans Grant. After defeating the Boss from the freight elevator, the dog tag is left behind, on the treadmill.
#12 Lieutenant Mat Shuggart. After grabbing the parka, go up the ladder next to where you came out. Up there you should see the dog tag before the bridge across to the corpse and the detonator.
#11 Second Lieutenant Chris Ditter. After coming in the Filtration Plant through the tool shed (you came in a by a ladder), make your way to the left. There should be a slope with a little bit of ledge. Climb across that ledge and make it to the platform across. Get up on the little bit higher platform. Under the platform, is the dog tag.
#9 Officer Cadet Ed Collate. After getting the dog tag receiver unit, duck under the platform next to the staircase. Slice the trip wire, then collect the goodies: A SPR4 magazine, shotgun shells, a flame thrower tank, and dog tag #9.
#6 Sergeant Robert Cameron. Near the wrecked train, where you first meet the watchdogs, use the dog tag receiver unit to find it.
#7 Sergeant David Murren. Once coming through the door of the train room, you should see a booth or something straight ahead. Slice the wooden crates to the left of it and you should see it to the right of the steel crates.
#13 Captain Kurt Gianini. Up the stairs, in the same room, there should be a vent in the area where you look down on the booth area. Once in, take the first right and go straight until you reach the end. Turn right and there they should be at the end.
#3 Private First Class Tom Taylor. In the room with the metal tag, same area as the other two above. You should find it by the metal tag.
#10 Officer Cadet Lance McLaughlin. After confronting Cindy, you should find this tag in the corner near her.
#2 Corporal Filel Sidalis. On the ledge outside, near Filel, there is the dog tag on the ledge. Use the dog tag receiver unit.
#14 Sergeant Roger Grigman. After defeating Roger, the dog tag should be just before the bridge. Also take his knife.
#15 Major Mike Madigan. After defeating Roger, go to where the wounded Madigan is located. Once the FMV sequence is over, his dog tags will be next to the elevator-like thing where he descended into the Facility.
#8 First Sergeant Ken Reschner. In the area with the ice camo car, the dog tag is in the corner of a little outcropping. You should now have 14 out of 15 dog tags.
Game Shark Codes
Master Code (Must Be On) EC8D3170 1445DC6C
Infinite Health 4C188B7E 145625DD4C1887F6 145625DD
0% Infection 4C1887FE 1456E7A54C188B82 1456E7A5
Infinite/Max Battery 3C188FD6 1456E7D53C188FDB 1456E7D5
Infinite MTS Vaccine 3C188FAC 1456E788
Infinite Recovery Unit A 3C188FA6 1456E788
Infinite Recovery Unit B 3C188FA7 1456E788
Infinite Booster Type A 3C188FAD 1456E788
Infinite Booster Type B 3C188FAA 1456E788
Infinite Shotgun Shells 4C188FD0 1456089C
Infinite Machinegun Ammo 4C188FDC 1456089C
No Reloads Machinegun 3C188F86 1456E70C
Infinite Grenade Rounds 4C188FCE 1456089C
Infinite Flamethrower Fuel 1C188FD4 1473E788
No Reload Flamethrower 4C188FD2 1456E788
Infinite Rockets 4C188FD8 1456089C
Have Climbing Spikes 3C188FA5 1456E7A6
Have Arctic Parka 3C188FA2 1456E7A6
Low Time 1C188878 1456E7A5
All Weapon Parts 1C188F8C 1355E6A61C188F90 1355E6A61C188F94 1355E6A61C188F98 1355E6A6
Have All Top Secret Files 1C188E48 1355E6A61C188E4C 1355E6A61C188E50 1355E6A61C188E54 1355E6A6
Have All Operation Manuals 3C188F07 1456E7A61C188F0C 1355E6A61C188F10 1355E6A61C188F14 1355E6A61C188F18 1355E6A63C188F1C 1456E7A6
Have All Classified Files 3C188E2F 1456E7A61C188E34 1355E6A61C188E38 1355E6A61C188E3C 1355E6A61C188E40 1355E6A61C188E44 1355E6A6
Have All Staff Logs 3C188F1D 1456E7A64C188F1A 1456E6A61C188F20 1355E6A61C188F24 1355E6A61C188E28 1355E6A61C188E2C 1355E6A64C188E30 1456E6A63C188E2E 1456E7A6
Have All Dennis' Memos 3C188FE7 1456E7A61C188FEC 1355E6A61C188FF0 1355E6A61C188FF4 1355E6A61C188FF8 1355E6A61C188FFC 1355E6A61C188F00 1355E6A61C188F04 1355E6A64C188F08 1456E6A63C188F06 1456E7A6