The United States Post Office has chosen Oshkosh Defense to build its next-generation mail-delivery vehicle, part of an effort to make the USPS more environmentally friendly by switching a portion of its huge fleet to electric vehicles.

Oshkosh Defense, a division of Wisconsin-based Oshkosh Corp., will assemble 50,000 to 165,000 of the new Next Generation Delivery Vehicles at its existing U.S. manufacturing facilities. It will get an initial $482 million toward retooling and building out its factory.

USPS described the deal, announced Tuesday, as the first part of a multibillion-dollar 10-year effort to replace its delivery vehicle fleet. It could be worth more tha $6 billion in total..

The choice of Wisconsin-based Oshkosh is a big miss for Ohio-based electric vehicle startup Workhorse Group, which put in an all-electric bid for the vehicles. Shares of Workhorse fell more than 47% Tuesday.

On Wednesday, Workhorse Group said it had requested more information from the Postal Service about the award.

Workhorse intends to explore all avenues that are available to non-awarded finalists in a government bidding process, the company said in a statement.

Workhorse shares were down about 10% in premarket trading on Wednesday. They had lost nearly half their value a day earlier after USPS announced Oshkosh the winner.

The postal service last updated its mail-delivery trucks 30 years ago, and there have been major changes in the service's operations since then. Traditional mail volumes have declined, while the service now delivers millions of packages from online retailers like Amazon that did not exist when the previous mail vehicle was introduced.

The new vehicles will have more room for packages, and will be updated with modern safety and driveability standards like cameras, airbags and collision avoidance systems. The vehicles will also be a combination of electric and gasoline powered, but the gasoline-powered new vehicles will have the ability to be retrofitted with new electric systems in the future.

This report contains material from Reuters and The Associated Press.