evidence: This year, the Defense Department asked Congress to approve a staggering $842 billion — nearly half of the federal government’s discretionary spending — to keep America safe in what the Pentagon says is an ever more perilous world. As House and Senate leaders negotiate the final number, it is unlikely they will spend much time discussing ways to prevent future debacles like the LCS. Such a conversation would cover hundreds of billions of misspent taxpayer money on projects from nearly every branch of the military: The F-35 fighter jet, deployed by the Navy, Marines and Air Force, is more than a decade late and $183 billion over budget. The Navy’s newest aircraft carrier, the Gerald R. Ford, cost $13 billion and has yet to prove it can reliably launch planes. And the Army’s Future Combat System was largely abandoned in 2009 after the military had dedicated more than $200 billion on a battlefield intelligence network meant to link troops, tanks and robots.