“Now someone has to take responsibility for the contract at the front end, so that if things go badly we know who to call on the carpet,” McCaskill said.

The law also requires the three agencies to conduct risk assessments to evaluate their use of contractors, to reduce reliance on private security firms and to establish databases to better track contractors’ performance and pricing.

Some of the measure’s provisions got watered down over time or cut entirely. The final version dropped language that would automatically refer companies accused of violating the law for suspension from government contracts, as well as a provision that would have forced firms that use subcontractors for more than half the work to identify the subcontractors in writing.

McCaskill had hoped to restrict the use of subcontracting, which can make it difficult to trace problems or pin blame. It also can add to costs, as primary contractors hire subcontractors who hire more subcontractors in turn, expenses ballooning with each new layer.

McCaskill said lobbyists for large contractors had successfully fought to exclude those provisions, however. The Obama administration also opposed a provision that would have required the president to provide Congress with a financial plan for any future war, and it threatened to veto the bill in part because of the language that mandated automatic suspension referrals for contractors charged with wrongdoing.

“Sometimes it’s boxing shadows,” McCaskill said of the push-back she encountered. “There’s big money in these contracts and there’s a lot of people who have made big money off these contracts, and clearly we are trying to stop the gravy train and I’m sure that there are people who wanted to keep it going.”

Ultimately, the changes appear to address many of the contracting irregularities that hampered America’s war efforts in the past decade, said Michael O’Hanlon, the director of research for the foreign policy program at the center-left Brookings Institution, a research center in Washington.

“Certainly the emphasis on competition, the emphasis on transparency with subcontractors, the emphasis on inspectors general, these are all welcome ideas,” O’Hanlon said. “I guess the hard part is going to be implementation.”

One unintended consequence might be to make it harder for the U.S. government to hire local companies for contracting work in war zones, a key counterinsurgency strategy, he said.

“Developing the intelligence on local subcontractors is actually fairly hard to do initially if you’re in a place you didn’t expect to go,” O’Hanlon said. “Those are the kind of practical issues that I would want to at least see if there could be ways to consider, assess or redress if it turns out in a future mission that they prove to be problems.”

Another criticism McCaskill acknowledged is that the revisions add red tape without adding funding, meaning that military commanders and other federal officials will have more paperwork to complete during wartime, but no new resources with which to do it.

“What we had in place wasn’t working, so having to cross a few T’s and dot a few I’s is a very small price to pay to save billions for taxpayers,” McCaskill said.