* Oshkosh shares surge 25 percent in post-market trading

* Shares of Navistar fall 10 percent

* Action comes after DOD awards $1.1 bln deal to Oshkosh

CHICAGO, June 30 (Reuters) - Shares of Oshkosh Corp (OSK.N: Quote, Profile, Research) surged in post-market trading on Tuesday after it won a $1.1 billion, fixed-price contract to build armored trucks for U.S. troops in Afghanistan.

OshKosh beat out a number of companies, including Navistar International Corp (NAV.N: Quote, Profile, Research), for the Pentagon award to build 2,244 of the new Mine Resistant Ambush Protected All Terrain Vehicles (MRAP-ATV).

The award was announced shortly after the close of regular trading on Wall Street.

Oshkosh shares were last trading at $18.22 in after-hours trading, up $3.68, or about 25 percent, from their close of $14.54 on the New York Stock Exchange.

Navistar shares, meanwhile, fell $4.40, or about 10 percent, to $39.20 after closing the regular session at $43.60.