A few notes to explain the different categories into which the flights have been divided, with a description of typical mission profiles derived from observation.
Transportation of special weapons between Kirtland AFB and overseas deployment sites (here, Europe).
The operation involves three C-17 aircraft: the primary load-carrier, and two 'spares'.
The first stage of the operation involves getting the C-17s into their initial positions, the primary at the deployment site in Europe, the spares at Kirtland AFB and RAF Lakenheath.
Next, the primary is (possibly) loaded with weapons to be returned to USA.
Then the primary flies non-stop to Kirtland AFB, being refuelled in the air along the way.
After (possibly) unloading at Kirtland AFB, the primary is (possibly) loaded with weapons for carriage to the deployment site.
Next, the primary flies non-stop back to the deployment site with mid-air refuelling.
Once the primary has safely returned to the deployment site, the 'spares' stand down and may return to their home base.
After (possibly) unloading, the primary is free to return to its home base, though this may be staged through one or more transport hub (e.g. Ramstein AB, Dover AFB).
Within the contiguous USA, special weapons are moved exclusively by road transport, so this category excludes such movements.
Note that the load status of the primary is not discernable from the mission profile, hence the relevant steps above are marked '(possibly)'.
Provision is made along several stretches of the route of non-stop flights for mid-air refuelling. Tanker support from McGuire AFB and RAF Mildenhall has been recorded for western and eastern parts of the North Atlantic respectively. This support has also involved 'forward positioning' tankers in advance of the flight to an airfield closer to, or otherwise more convenient for, the refuelling area.
On the (possibly-) loaded legs of the operation, the primary aircraft will fly only over the USA, the country of the deployment site being serviced, and other countries that have special arrangements with USA to allow these flights.
The role of the 'spares', it seems, is two-fold. First, they can replace the primary should it develop some condition that prevents it completing its mission safely. Secondly, should there be a serious incident while transporting special weapons (especially damage to the weapons) the spares can carry immediate response teams and their equipment to an airfield close to the incident site. Clearly, the spare at Kirtland AFB covers initial response in USA, the spare at RAF Lakenheath covers Europe. But should the incident take place in Europe, the spare at Kirtland AFB would be available to transport follow-on responders from DoE NNSA and USAF at Kirtland AFB.
Other cargoes relating to special weapons, transported between Kirtland AFB and deployment sites in USA and overseas (here, Europe).
The operation involves a single C-17 aircraft.
In the first stage of the mission, the aircraft flies to Kirtland AFB.
The second stage sees the aircraft flying to a deployment site, via a staging airfield for destinations in Europe (Dover AFB, McGuire AFB). Several overseas deployment sites may be served in a single mission over several days. Between delivery legs, a staging airfield may be used, e.g. Ramstein AB.
Once all destinations have been visited, the aircraft will return to Kirtland AFB, again for overseas deployment sites via a staging airfield.
Finally the aircraft will return to its home base.
The same strict overflight rules as for category 0 also apply in this case. For this reason, a mission serving Europe will usually be restricted to either northern or southern Europe. Flying between the two regions involves flying west over the Atlantic, then north or south, then east into the destination region (see this mission).
Some cargoes to deployment sites within the USA are delivered by flights by DoE NNSA aircraft (and probably road vehicles). Since the DoE does not operate outside the USA, it can be assumed that such cargoes (if applicable to the deployed weapons) are delivered by these USAF flights.
Other cargoes transported between USA and overseas deployment sites (here, Europe); itinerary does NOT include Kirtland AFB.
Flights are made by the same aircraft and aircrews as category 0 & 1.
Several deployment sites may be visited in a single mission.
Overflight of “friendly” countries that have not entered into special arrangements with USA is permitted, simplifying movement between northern and southern Europe (see this mission). This can be interpreted as meaning that the cargo is not hazardous.
Use of staging airfields is made throughtout the mission, including those operated by US armed forces in countries that do not have arrangements with USA for basing or moving special weapons (e.g. Rota AB in Spain).
Understandably, there are strict minimum requirements for the proficiency of aircrews involved in all these flights, and for the maintenance of aircraft and other equipment involved. It must also be stressed that there are similar security requirements. Aircrew members involved will acquire significant knowledge about location, types and numbers of special weapons deployed outside USA, and thus will have been subjected to intense scrutiny by security agencies before being assigned to units peforming these missions. These are good reasons why only a single unit is performing these special missions.