To be honest, we don't really know how much a military project really costs, so most just means most we could determine. Blame money being hidden in $300 plungers.
Most expensive also doesn't include projects that yielded few positive results, like the theme parks in Vietnam...
10.) General Dynamics Ohio-Class Submarines
The US Navy has 18 of them, and while Russian Typhoon and Borei-class submarines are bigger, the Ohio-class can carry the most (nuclear) missiles. That comes at a price. Stig-a-saw-us wrecks has a costs list: