Assigned to handle arms purchases for the British government, MacGregor came to the U.S. during World War II. Sensing a fertile climate for business, MacGregor stayed in the U.S. after the war and became the CEO of American Metal. Through his shrewd cost management techniques and diversification efforts, he built AMAX into the third largest mining operation in the United States. From this success, he moved back to Britain where, in his 70’s, he reorganized the British Steel Corporation.