Time to reshuffle your cards, defense investors.

Fresh off its victory on the $40 billion KC-X Tanker contract, No. 3 national defense contractor Northrop Grumman (NYSE:NOC) decided to shift its focus a bit yesterday, when it agreed to sell off its "Electro-Optical Systems" (EOS) unit to fellow contractor L-3 Communications (NYSE:LLL).

What is EOS, exactly? According to Northrop's website, it's a business built from integrating "the assets and resources of five premier night vision companies into one dynamic division, Northrop Grumman Electro-Optical Systems." EOS sold $190 million worth of such night-vision gear last year. Yet L-3 is getting the whole ball of wax for a mere $175 million.

Is that a steal of a deal, or a rip-off? Hard to say, without knowing precisely what margins Northrop has been reaping from the business. What I can tell you is that the price looks objectively fair if L-3 can extract its own usual profit margin from the Northrop unit. Right now, L-3 sells for just a little more than 0.9 times sales -- which, coincidentally, is exactly the price-to-sales ratio it's paying for the EOS unit.

Worst case, best case
The worst case, therefore, is that L-3 is paying a fair price for the EOS business and improving its ability to compete with the whole range of defense contractors that offer similar night-vision technology -- General Dynamics (NYSE:GD), Raytheon (NYSE:RTN), Silicon Graphics (NASDAQ:SGIC), and Microvision (NASDAQ:MVIS), to name just a few.

And the best case is that L-3 is robbing Northrop blind. You see, Northrop earns about a 9.4% operating margin across its many revenue streams. But within the electronics shop in particular, where EOS used to be housed, Northrop has been pulling down a hefty 11.8% margin.

The way I look at it, L-3 appears to be snagging one of Northrop's most profitable operations -- a business that routinely earns more than L-3's own 10.4% operating margin -- and is paying no more than an average price for it. I see a lot to like in this deal.

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