Investor Carl Icahn issued a scathing open letter to shareholders of Oshkosh Corporation today, just a few weeks before the annual meeting and director vote scheduled for January 27.

The letter comes in response to a letter issued earlier this week by Oshkosh Chief Executive Charles Szews and Chairman Richard Donnelly, criticizing Icahn.

Icahn, who owns more than 9 percent of Oshkosh shares, has nominated six directors for the corporation’s board and reiterated support for his nominees, defendeding his ability to steer Oshkosh's strategy.

“I believe that my six director nominees have the necessary skills, experience and objectivity to help fix the problems at Oshkosh,” wrote Icahn. “I think change is necessary and crucial for the future success of Oshkosh.”

Icahn’s role with the corporation has been under intense scrutiny since he bought a 10 percent share in competitor Navistar International Corporation, and stressed the two companies need to explore synergies.

"Mr. Icahn has not demonstrated that he has a plan or a team that can lead your company and deliver value to all Oshkosh shareholders," wrote Szews. “Mr. Icahn is seeking to control nearly half of the Oshkosh board, yet has provided no substantive ideas or analyses to enhance value for all shareholders."

According to Icahn, the total enterprise value of Oshkosh has dropped by $500 million over the last three years, but Szews argues for support due to a 3-year total shareholder return of 45 percent.

Oshkosh designs and builds specialty trucks and access equipment for defense, emergency services, and commercial use, and is one of the top federal contractors in the U.S.