 They were phased out from military usage in the 1980s with the introduction of the HMMWV series vehicles.The HMMWV was, however, unable to fulfill the role of the Mule, so the M-Gator, a military variant of the popular John Deere Gator vehicle, was introduced.The M274 Mules were often outfitted with a wide array of weaponry, especially in the Vietnam War.