The Beatles Yellow Submarine by Hot Wheels.
On first glance, not the most military of subjects.
But consider it repainted in gray and with USN markings.
It has rollers on the bottoms. So I consider it not unlike those Soviet submersibles that used to proble Swedish national waters back in the days of the Cold War.
So while it could float along, it usually would drive along the bottom, making it harder to find on sonar.