Can a LAPD officer tell me that he is arresting me for being in the US army? I want to file a lawsuit against the LAPD

You were arrested for a DUI, not for being in the Army. I have no idea about why they would let you go with a warning. If your BAC is .08 or above they have no choice but to arrest you.

I agree with my colleagues; you were arrested for suspicion of DUI, not for being in the army. Whether the LAPD had enough probable casue to do that is something you might want to look into, especially since they were willing to let you go with only a warning? Consult with a local attorney prior to your first court date.

the fact of the matter is if you were DUI they had the lawful ight to arrest you. if this occurred it's unlikely you'll ever get them to admit it. but again being DUIgives them the right to arrest you

Now you can wonder about whether the result would have been different if you had said "SEMPER FI !!" (but always tell the truth). Police Officer force composition, based upon my observations, are more highly populated with ex-marines than ex-army, despite the fact that the army is much bigger in numbers. Are MARINES more likely to cut another MARINE a break?