Traton, Volkswagen's global truck unit – with often-declared aspirations to become the world's No. 1 truckmaker – has made its long-expected bid to buy out Navistar.
The truck conglomerate, which already wholly owns Scania and MAN, has held a 17% stake in Navistar – the manufacturer of International trucks – since 2016.
It has offered to buy the balance of the American company for $US35 a share. That would put Navistar's total valuation at $US3.5 billion, according to US reports – and would cost Traton upwards of $US2.5bn.
Since taking its stake in Navistar, Traton has collaborated with the US company on a number of research and development projects. The alliance has also seen Navistar introduce a MAN engine as the International A26 and a prototype medium-duty etruck.
In a press release, Traton said that as the global commercial vehicle industry evolves, it believes that the proposed transaction is "the logical next step."
The combined company would be better able to meet the demands of new regulations and rapidly-developing technologies in connectivity, propulsion and autonomous driving, it said. 
Traton CEO Andreas Renschler said: "Over the past three years, we have benefitted from a highly collaborative and productive strategic alliance with Navistar.
"As the market continues to evolve, we believe there are compelling strategic and financial benefits to a full combination of Traton and Navistar. The proposed transaction would create a leader in commercial vehicles with global scale and a strong portfolio of leading brands and cutting-edge products, technologies and services, while delivering immediate and substantial value to Navistar stockholders."
Navistar said it would it would "carefully review and evaluate the proposal."