What may weigh more than an M1 Abrams tank and carry 12 soldiers? The Army’s Ground Combat Vehicle. New weight estimates for GCV, released this week by the Congressional Budget Office, will likely go over like a lead ballon with the program’s critics in Congress and in the Army itself.

Depending on the model and add-on armor package, an M1 weighs 60 to 75.5 tons. According to the CBO report, the General Dynamics design for the GCV weighs 64 to 70 tons. BAE s proposal is still heavier, at 70 to 84.

There’s a tactical reason for all this weight: It’s armor. The Ground Combat Vehicle is supposed to replace the Army’s current frontline infantry carrier, the M2 Bradley, carrying more foot troops in back — nine instead of six — and protecting them better against everything from rocket-propelled grenades to roadside bombs. Even the most heavily uparmored models of the M2, at almost 40 tons, proved too vulnerable for the worst streets in Baghdad during the “surge,” so commanders often sent 70-plus-ton M1s to clear the way. Even some of those M1s blew up, in part because the insurgents could build huge improvised explosive devices, in part because the M1′s armor is mostly on the front to protect against enemy tanks, not on the underside.

So there is some logic to making any future troop carrier at least as heavy and well-protected as the M1 tank — especially since it would have more American lives inside. It’s just not the direction the Army was trying to go with GCV.

Two years ago, when the Army withdrew its original Request for Proposals for the GCV and revised its requirements, part of the reason for the change was shock at the sheer weight of the proposed designs: 50 tons for just the basic vehicle, up to 70 with all the optional add-on armor packages for the most dangerous missions. “You’re telling me this is going to be 70 tons, which is the same as an Abrams,” Gen. George Casey, then Army Chief of Staff, said incredulously at the time, in an interview with Defense News. Now it looks like the revised requirements have led to a vehicle that’s even heavier.

The CBO report repeatedly describes the proposed GCV as weighing “from 64 to 84 tons,” already an extraordinary figure, but a few lines on page 35 of the 60-plus-page document divulge details of the two competing designs, down to the CBO’s estimates for ground pressure in pounds per square inch.

The bottom line: BAE’s is bigger. That’s not a good thing given that cost tends to go up, and maneuverability to go down, as a vehicle’s weight goes up. That’s also a surprise, since BAE took the bold step of designing its Ground Combat Vehicle with a hybrid-electric drive, which by eliminating heavy mechanical components like the drive shaft can normally be lighter than comparably powerful conventional engines. In fact, BAE vice president Mark Signorelli told reporters at the Association of the US Army’s annual conference last month that going hybrid saved BAE’s GCV design three tons.

Yet CBO says the basic configuration of the hybrid-electric BAE design weighs in at 70 tons, compared to 64 for the conventionally diesel-powered General Dynamics. That’s a nine percent weight difference between designs supposedly meeting the same minimum requirements. At “potential maximum weight,” which the report does not define, General Dynamics maxes out at 74 tons and BAE at 84 — although that may simply mean the BAE version can add more armor than GD’s, which would be an advantage.

That’s the implication in the Army’s statements to Breaking Defense. GCV program spokesman Sam Tricomo said in an email that “the 64 to 84 ton weight range identified in the report does not represent a fully informed fact, as industry continues to resolve the entire range of GCV requirements, including weight, with technical solutions.” Further, Tricomo wrote, “the report does not clearly specify that the weight range quoted represents provisions for growth built into the development.”

In other words, (1) the contractors are working to bring the weight down from what’s in the CBO report, and (2) CBO’s highest figures — that “potential maximum weight” — reflect possible future configurations that are heavier than what the Army currently requires.

(The authors of the CBO report did not respond to AOL’s request for clarification by press time).

There’s a case to be made for a massively well-protected troop carrier for the most dangerous missions — urban warfare against well-armed guerrillas a la the Chechen defenders of Grozny, for example — but it’s not necessarily a case the Army’s ready to make, not yet.

“We’re about halfway through the tech development phase,” Col. Andrew DiMarco, the Army’s program manager for GCV, told reporters last month at the AUSA conference. BAE and General Dynamics are currently building components, testing them, and occasionally blowing them up to test their levels of protection. Each firm has a $450 million, two-year technology development contract that runs until August 2013.

The next stage would be engineering and manufacturing development (EMD) awards to one firm, both of them — or neither: The Army plans on “full and open competition,” DiMarco said, which means a third competitor could win an EMD contract without having won a technology development award, as occurred recently on the Joint Light Tactical Vehicle (JLTV). While BAE and General Dynamics between them control the US tracked vehicle business, the Army has also evaluated foreign war machines like Israel’s 60-ton Namer, which although very much a second choice might become more patalable if the US designs prove too heavy and expensive.

The Army had planned to award two EMD contracts to encourage competition before it made its final choice, but Inside the Army reports that the service is now under pressure to award only one — which would save money in the short term but sacrifice the long-term potential for savings from competition. That decision would have to be made before the FY 2014 budget is submitted in February.

With the vehicle designs and the contract structure both still evolving, GCV continues the long and painful saga of the Army’s attempts to modernize its armored vehicle fleet, which traces back through the Future Combat Systems program to the Crusader howitzer, both long since cancelled. As budgets tighten, the vultures are circling GCV as well. If the Army wants this weapon, it has to get it right — and it has to fight for it.

“They’ve gone through endless analysis and decision reviews” on GCV, said Scott Davis, the Army’s Program Executive Officer for all ground combat systems, speaking alongside Col. DiMarco last month at AUSA. “I’ve seen lots of times where I thought programs were solid — and things change.”