The U.S. has a new law that is meant to eliminate the cost overruns and delays in defense procurement projects. The 2009 Weapon Systems Acquisition Reform Act restores techniques that have failed in the past and adds additional layers of bureaucracy to the acquisition process.
There are three reasons for most cost overrun and delay situations. These are problems that no one likes to even admit exist. First, there's the Pentagon tradition of "low balling." When competing to get a contract, the firm with the lowest plausible price gets the job. This has been going on for generations. Everyone knows that, once work begins, the manufacturer will deploy his publicists, lobbyists and accountants to explain that unforeseen events have caused the actual price to be much higher. Angry speeches will be made in Congress, embarrassing stories will appear in the media, and the extra money will be found. Everyone swears that it won't happen again. But it always does.
Another problem is that most new weapons use new technology. New and innovative always costs more. Even when there is new technology taken from the commercial sector, there are always problems adapting this commercial tech to military use. Controlling this has proved difficult, because it's a worldwide problem, and if one nation backs away from untried technology, while others continue to do so, the risk takers are likely to obtain a large battlefield advantage.
The biggest problem is another old one, and that's the tendency of the military to keep coming in with "essential changes." These cost money. The generals and admirals know they are at fault here, and have tried to back off in this area. But, like low balling, it's a hard habit to break. This sort of interference is much less of a problem in wartime, but no one has been able to recreate that atmosphere in peace time. Sometimes, the new changes are not from the military. New environmental rules often require changes for systems under development. These mandates often are accompanied by the threat, or reality, of lawsuits and Congressional investigations.
Lastly, we have the politicians. The Pentagon learned, over a century ago, that if you want to maintain Congressional support, make sure that the defense money goes into the right Congressional districts. Some politicians won't wait for the Pentagon to make these decisions, but will constantly lobby for a piece of the action in their state or district. Some politicians insist on weapons being built mainly because it creates jobs, and happy voters, back home. Congress has a hard time passing a military procurement reform law that will deal with this angle.
You can't fix the problem if you can't even admit what it is.