Mr. Donovan. Well, I did not witness the changing in any other squadrons, but it would have to be, because the code is obviously between two or more units. Therefore, the other units had to change it. These codes are a grid, and two lines correspond.
And he gives the grid that you want, and he reads back "AB," or whatever the reply is supposed to be, the authentication is supposed to be.
Mr. Ely. Are authentication codes changed from time to time as a matter of course?
Mr. Donovan. They are changed from time to time, that is right.
Mr. Ely. Are they changed even if there is no specific incident which elicits the change?
Mr. Donovan. They are methodically changed anyway. There are some things which he knew on which he received instruction that there is no way of changing, such as the MPS 16 height-finder radar gear. That had recently been integrated into the Marine Corps system. It had a height-finding range far in excess of our previous equipment, and it has certain limitations. He had been schooled on those limitations.
It cannot operate above a given altitude in setting—in other words, you cannot place the thing above a given terrain height.
He had also been schooled on a piece of machinery called a TPX-1, which is used to transfer radio—radar and radio signals over a great distance. Radar is very susceptible to homing missiles, and this piece of equipment is used to put your radar antenna several miles away, and relay the information back to your site which you hope is relatively safe. He had been schooled on this.
And that kind of stuff you cannot change.
Mr. Ely. Did Oswald have any kind of clearance?