Making planes, tanks, and ships isn't cheap. Now factor in the cost of personnel, housing benefits and operations and you have a defense budget that balloons into the billions.
Related: Defense budget spotlight: What do weapons really cost?
In 2011, the U.S. government spent about $718 billion on defense. That's nearly half of all military spending on the planet. The other top 13 nations combined spent $695 billion.
While the yearly budget is spread out according to defense needs, some projects take the lion share. Case in point are weapon systems like the Virginia Class Submarine with a procurement cost of $76.6 billion and the V-22 Osprey at $95.2 billion. Although costly, they aren't the most expensive military mega-projects of all time. Here's the list:
1. Nazi Germany's Atlantic Wall
Final cost: unknown
Although the final cost was never determined, the French portion alone would have cost $200 billion when adjusted for inflation.
2. National Missile Defense
Cost: over $300 billion and still rising.
3. DDG-51 Guided Missile Destroyer
Procurement cost: $87.3 billion
4. USS Gerald Ford Aircraft Carrier
Per unit cost: $13 billion
5. F-35 Strike Fighter
Current cost: $400 billion
Estimated total cost: $1.5 trillion