It wasn't supposed to be a happy day for Force Protection (NASDAQ:FRPT) shareholders.

Just a couple of weeks ago, the news had come down from HQ: Force Protection is no longer in the running to build America's Next Top Humvee. Instead, the Pentagon will choose its JLTV variants from offerings manufactured by General Dynamics (NYSE:GD), Lockheed Martin (NYSE:LMT), and Navistar (NYSE:NAV), and their various partners.

Joining Force Protection in the losers' circle: Boeing (NYSE:BA), Raytheon (NYSE:RTN), Northrop Grumman (NYSE:NOC) -- basically, everybody who's anybody in the world of defense, and not named General D, Lockheed, or Navistar.

But life goes on, and even though Force didn't win the JLTV contract, it still has work aplenty -- as yesterday's earnings report showed. We learned that Force's third-quarter sales leapt 66% in comparison to last year's Q3, while the company earned a $0.29-per-share profit in contrast to last year's penny-a-share loss. Turns out that although Force didn't win the Humvee contest, it still has an awful lot of already-built MRAPs to service and repair for the military. Indeed, CEO Michael Moody credited this "growth in spare parts and services revenues" as a major factor in Force's Q3 growth.

Meanwhile, Force continues churning out Cougar MRAPs and Buffalo mine-clearing MRAPs for additional revenue. In the process, it's growing its base of units that will need servicing in the future.

Evolve or die
But speaking of minefields, Moody made a point of giving us a heads-up that "deliveries under the MRAP vehicle acquisition program come to a close during the upcoming fourth quarter." Force's funded backlog now contains fewer units to produce in the future than it manufactured in Q3 alone.

And so we return to the eternal question concerning this company: What will it do when the MRAP contracts stop coming? Well, servicing and repairing existing MRAPs provides part of the answer. The $72 million in revenues it generated from this area in Q3, if continued quarter in and quarter out, will suffice to justify the company's approximately $205 million market cap already.

But for the stock to resume its growth-stock ways, Force's continued investment in research and development -- building a new "cargo" version of the Cougar, for example, as well as a new "restricted terrain" variant -- must meet more success than did the company's Cheetah. Otherwise, Force Protection could begin looking quite vulnerable indeed.

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Fool contributor Rich Smith owns shares of Force Protection and Boeing. The Motley Fool has a disclosure policy.