Oval shaped object hovered in sky and then flew off in a diagonal direction EXTREMLY fast and disappeared

It was right around dusk. Me, my sister and a friend were playing in a park when we saw what looked like lights on an airplane in the sky. The strange thing was that it was not moving. We then thought that it was a helicopter. It hovered in the sky for about 20 seconds and then made extreme radical diagonal moves. It then hovered again for a few more seconds. Then we saw 3 large Military/Air Force planes approaching. The oval shaped object then flew off in a diagonal direction EXTREMLY fast and disappeared. The Military planes (looked like the kind with radar) flew directly overhead. We ran home and told our father and he said that it was probably just an airplane, but he didn’t see what we saw