Comment by mike_d

> is there any definitive evidence of the actual transport mechanism?

I can tell you from first hand experience that moving high value items isn't as exciting as you'd think.

ULDs are the standardized shipping containers of the sky. You can rent ones that have an inner armored layer and tamper evident seals. They fly as commercial cargo, usually on the flag carrier airline if its a government load. No special rituals or armed guards. Shipments are broken up so the loss of a single aircraft is at most $5 or $10 million.

There are some highly specialized aircraft that transport full loads but they tend to be closer to the supply side, moving bulk gold or diamonds from remote mines for processing.

Cash is the interesting exception (most non-US currency is produced by commercial printers) where a country will send its military to go pick up one big shipment.