REALITY CHECK
First, do not turn a video transition into a submarine.
One of the best-known alleged transmedium cases, the 2013 Puerto Rico infrared video, was resolved by AARO in 2025. AARO assessed with high confidence that the objects did not display transmedium behavior and with moderate confidence that they were sky lanterns.
That is exactly why the technology question must remain conditional. A track near the ocean, a disappearing thermal contrast, or an apparent crossing of the horizon does not by itself establish entry into water.
The engineering only becomes interesting after independent geometry and sensors show the same object actually crossing the interface.
WHY WATER IS MEAN
The density jump is enormous.
At sea level, liquid water is roughly three orders of magnitude denser than air. A vehicle designed to move efficiently through one medium generally does not get the other for free. Fast entry into water can generate enormous transient loads, spray, pressure waves and cavitation. Fast underwater motion generates drag and acoustic consequences very different from flight.
Humans solve this by changing speed, shape, control mode and propulsion. Aircraft become terrible submarines for reasons that continue to offend science-fiction budgets.
KNOWN PATH 01
Slow down and accept the interface.
The simplest real transmedium vehicle behaves differently in each domain. It flies, slows dramatically, enters the water under controlled conditions, then switches to underwater propulsion. That is technologically difficult but unsurprising.
If a UAP report describes exactly that, no exotic physics is required. The mystery would be identification, not mechanism.
KNOWN PATH 02
Supercavitation cheats underwater drag by making a gas cavity.
At high underwater speed, a body can be surrounded by a vapor or gas cavity so that much of its surface contacts gas rather than liquid. Humans have demonstrated supercavitating projectiles and torpedo concepts.
That helps with drag. It does not make the vehicle silent or invisible. Cavitation is noisy. Maintaining and controlling the cavity is difficult. Maneuvering is constrained, and entry into the cavity regime has its own transient behavior.
An alien implementation could be vastly better, but the general signature would still tend to involve bubbles, acoustic energy, pressure disturbances or some other evidence that water has been violently rearranged.
KNOWN-ISH PATH 03
Actively manufacture the boundary layer.
Instead of relying on passive cavitation, an advanced vehicle might inject gas, vaporize water, use plasma, heat the surrounding fluid, or electromagnetically manipulate conductive seawater to create a lower-drag envelope.
Pieces of these ideas exist in real fluid dynamics and magnetohydrodynamics. None currently give us a compact vehicle that can move from atmosphere to deep water at aircraft-like speed with minimal disturbance.
Still, this class of mechanism is technologically intelligible. It says: do not force the hull through the medium unchanged; engineer the medium around the hull.
SPECULATIVE PATH
Prevent the surrounding matter from interacting normally with the craft.
The strongest versions of transmedium UAP stories imply something stranger than superior hydrodynamics. They imply that air and water somehow fail to impose the expected drag and impact loads.
A hypothetical field that displaced matter ahead of the craft, altered local pressure, changed effective inertia, or enclosed the vehicle in a region with unusual spacetime geometry could in principle address that class of observation.
We have no demonstrated engineering capable of doing this. There is no verified “force field” that lets macroscopic vehicles ignore fluid mechanics. This remains speculative physics, not secret knowledge wearing a lab coat.
THE SIGNATURE TEST
Water gives us more ways to catch the lie.
A genuine high-speed water entry should be investigated with synchronized optical imagery, infrared, radar, sonar, hydrophones, surface-wave monitoring and, where possible, pressure sensors. If a craft enters at speed, the ocean should respond.
If supercavitation is involved, look for bubbles, void structure and acoustic noise. If intense heating or plasma is involved, look for steam, thermal anomalies, conductivity changes and chemical products. If the object supposedly passes through water with none of those effects, then the burden of proof rises sharply because the claim is no longer merely “advanced submarine.”
BOTTOM LINE
Transmedium is a physics claim, not a visual vibe.
If a future case provides calibrated, simultaneous air and underwater sensing that tracks the same object through the interface without expected hydrodynamic effects, that would be extraordinary evidence of extraordinary engineering.
Until then, disappearing against an ocean background is not enough.
Prove the interface crossing. Then interrogate the fluid.
Source trail: AARO Puerto Rico case resolution · NASA UAP Independent Study · AARO public UAP report documents