Its really simple, whether its weapons systems or food or shoes, international trade theory states that trade is going to be based on comparative advantage between nations. I happened to study defense policy in depth as part of my grad program, just lucky I guess to be in DC and have classes taught by R+D guys at the Pentagon. We are not isolationist as much as you guys would like us to be. So whether or not we CAN make the goods is not the issue. If it costs us a trillion dollars to build something when you take into account R+D, plant and equipment, training etc, is that better than buying it from an ally?
djv, I guess your logic is that we should never import anything, we should make everything right here? Since you brought it up, the M1A1 Abrahms, the most deadly high tech tank in the world, you couldnt be more wrong about. It comes from a lot of other places. The main weapon on the M1A1 is the 120mm M256 Smoothbore Gun - it was designed and built in **Germany** by Rheinmetall GmbH. The armor was designed with the help of the British Ministry of Defense and patterned after their Chobam armor. The digital fire control systems are designed by and come from Canada, a company now a division of General Dynamics - Canada. There is at least one other major system on it that is from another country as well. Is this what you meant by "Our tanks with all the high tech do not come from any other place."
Its tough to have an argument about trade or economics here when the "USA rules, all the other countries suck" attitude pervades. Nothing I can say is really going to convince you otherwise.