Finally Found a DoD Project That's On Budget and On Schedule

It's the AH-64 Apache Block III Upgrade.

This is actually a non trivial upgrade:

The Block 3 improvements are pretty fundamental, requiring a new airframe, more than 1 million lines of code, a new transmission system, longer range and automatic recognition radar, UAV connectivity, the ability to communicate with a much wider range of platforms (but not stealthy aircraft), software that will help the air crew make rapid decisions and a host maintenance management systems that are expected to reduce the average flight hours lost to fixing and maintaining things by 30 percent.

And it appears that it's working because of the basics, keeping up good lines of communications and avoiding requirement creep.

That last one seems to be the biggie in defense procurement fiascoes, which is why the entire spiral development model is problematic.