These projects feed into an ongoing effort to explore ways of using artificial intelligence (AI) to enhance the American military's capabilities.
But Shahahan said legacy systems would not "go away overnight" and that it was a question of finding a balance and using AI where it could make things more efficient.
"The last thing I would claim is that carriers and fighters and satellites are going away in the next couple of years," he said.
Earlier this year, Elon Musk also entered the discussion, telling the audience at a military conference in Orlando, Florida, that the "fighter-jet era has passed".
Mr Musk said the F-35 fighter jet's competition should be a drone, remotely-controlled by a human with manoeuvres augmented by autonomy.
"The F-35 would have no chance against it," he tweeted.
Lt Gen Shanahan said that the military should be absorbing the best lessons from work on autonomous cars in the commercial sector.
But he warned that among manufacturers, 10 companies spending $13-17bn on research over the last decade had still not developed a Level 4 autonomous vehicle.
Level 4 vehicles are those that no longer require a human driver's attention for safety.
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