The Pentagon has spent at least $58 billion over the past two decades on weapons systems that seemed like a good idea at the time, but never made it off the ground, or even off the drawing board.

The eye-popping figure is buried in a Pentagon report released this week from Undersecretary of Defense for Acquisition, Technology and Logistics Frank Kendall.

The internal review of the Defense Department's acquisition performance contains a chart of 23 big-ticket weapons programs that were started, initially funded, and then canceled after billions were spent going back to 1997.

The biggest boondoggles were the Army's ill-fated Future Combat System, which accounted for more than $20 billion of the total, and the RAH-66 Comanche reconnaissance/attack helicopter on which $9.8 billion was invested before the plug was pulled.

Those two programs alone account for over 50 percent of the total that had to be written off as "sunk costs."

Pentagon officials insist not all of that money goes down the drain, because even when programs are canceled, the technology that was developed along the way can be used in other weapons systems.

The Pentagon report also noted that many of these programs were far along in their development before a decision was made to stop throwing good money after bad. Eight of the 23 spent all the money budgeted for them, before they were killed.

Other big-ticket disappointments include the NPOESS satellite at $3.7 billion, the VH-71 presidential helicopter at $2.7 billion, and the JLENS air defense blimp at $2.5 billion.

A chart of all the programs can be found on page 107 of the report.