In the United States' system—and the United States arguably takes its security perhaps the most seriously among all the NATO partners, for obvious reasons—the service chiefs, the head of the Navy, the Army, the Air Force, the Marine Corps and the Coast Guard, each have purchasing authority under military officers. They don't go through the same slightly labyrinthian maze of approvals required where everyone has to not say no in the Canadian system. That takes time, and a lot of time.
In the American system, it's arguably a lot faster, more effective and with better output, based on the size of the American forces and the quantities of money that are currently available to spend on a program.