These patents & papers were published in the past year or so.
Hydrid Craft Using Intertial Mass Modification Device–article–pais2017.pdf
Room Temperature Superconducting System for use on a Hybrid Aerospace-Undersea Craft–article– pais2019.pdf
US10144532-Pais-Craft Using An Inertial Mass Reduction Device.pdf
US20180229864A1-Pais-High Frequency Gravitational Wave Generator.pdf
US20190058105A1-Pais-Piezoelectricity-Induced Room Temp Superconductor.pdf
Easily available on the net.
Would explain such sightings.