Well, after studying the now famous contrail photographed by Steve Douglass some years ago now, i decided to see if these vapour trails were made just by Secret Aircraft or possibly normal Jet engined aircraft such as Fast Jets and Airliners.
After several years i have seen many many vapour trails that resemble the famous trail and some are nearly exactly the same. HOWEVER, they were all made by normal military aircraft and on some occasions by large airliners.
Below is what i think about the whole 'Donut-on-a-rope' contrail story.

When i first saw Steve Douglass' photo of the vapour trail, i was immediately fixed on proving that his trail and many others similar were made just by normal everyday aircraft with jet turbofan engines.
I have the same hobby as Steve Douglass, i have been monitoring aircraft for some years and for most of my life i have been a keen Military Aviation enthusiast, lucky enough to see near nearly all of the worlds air arms aircraft flying.
I spend hours sitting on top of hills with my scanners and binoculars watching and listening to military aircraft. If i'm not on the hills, i'm at home scanning aswell...
Living in an extremely active MTA(Military Training Area) and a dedicated Low Level Training Area i get to see everything from nearly all NATO Air Arms flying very low level to huge dogfights and air intercepts medium - high level. I also see everyday, the British AFFTC aircraft on trials out of Boscombe Down.

Like Steve, wherever i go, i take my camera and binoculars with me - just in case - i do something interesting.
There have been many times i have seen similar vapour trails to the D-O-A-R trail but have not taken photo's of it...instead looking in my Bino's at the aircraft making it....
A good few times the aircraft making these trails have been Boeing 747's coming back and going to the Eastern United States. I live directly under one of the main air-routes to and from the States and England so i see an awful lot of civil jet liners overflying.

However recently i have had the brains to start taking photographs of these strange trails made by the jet engines.
Within two weeks i managed to catch two vapour trails identical to the one Steve Caught a few years ago but from TWO different aircraft.

Below is the first photograph i shot when on a hill near where i live. A Favourite place to watch military jets Below in the valleys and dogfights above you.
details are below
 

LOCATION	South West England, County of Devon
AIRCRAFT TYPE/ Callsign/ Sortie	Royal Air Force Harrier GR7 on a test flight from BAe Dunsfold working in conjunction with RAF/DERA Boscombe Down AFFTC. Callsign used was 'HAWKER BRAVO'
AIRCRAFT MOVEMENT	Harrier GR7 was turning a variable arc from east - west to west - north at time of shot
DAY TEMPERATURE	Wednesday Middle of  June 78°F measured with mercury
WIND	South Westerly 5 kts Ground. Approx 30kts at aircraft altitude. Same Direction
WEATHER	Nill: Very Sunny with light high level variable cloud
TRAILS	Trails stayed aloft for very short time. not enough cold air and too strong a wind which broke up and dissipated the trails in a short period. Maximum 3-10 minutes.
TIME	11:28 Local Time (BST)

Albeit much smaller due to the atmospheric conditions on the day...the trail only lasted a few minutes.
Looking at the photo you can clearly see the 'puffs' on a string of trail made by the engine. A Harrier has only a single powerful jet turbofan and is not reheated.
No Secret Plane here. and no PDWE..thats for certain!

Photo Copyright ©2000. Richard Cliff.  All Rights Reserved.
The same but without the main photograph.
Photo Copyright ©2000. Richard Cliff.  All Rights Reserved.

Below is another photo, more recent and approximately two weeks after the one above.
Location was exactly the same spot as above also but the vapour trail was directly above me, with me having to really bend over to get the photo properly.
 

LOCATION	South West England. County of Devon
AIRCRAFT TYPE/ Sortie / Callsign	Aircraft was a Defence Evaluation and Research Agency Jaguar GR3 from the AFFTC at Boscombe Down. Flying with the Empire Test Pilots School. Sortie was a high speed flight test and spin/stall trials. Callsign was TESTER 07
AIRCRAFT MOVEMENT	The Jaguar was in a high speed, high sub-sonic flight test going east to west towards a designated Stall, Spin trials area......Aircraft was Directly above me.
DAY TEMPERATURE	Tuesday Beginning of July. 82°F
WIND	2 kts Ground wind with approx 10-15kts aircraft altitude. Southwesterly
WEATHER	Nil weather. Sunny day, no cloud in sight. High pressure.
TRAILS	Trails lasted approx 5 mins. Not enough cold air to keep the trails aloft.
TIME	13:46 Local time (BST)

This trail was very long, atleast 5 times longer than the previous one made by the Harrier.
It was not trailing until he became directly above me...from then on he trailed until i could not see him visually anymore.
Again.....no Secret Black Budget aircraft here and no PDWE! but only a Jaguar Strike aircraft.
Seen clearly, but not as clear as the previous is the characteristic 'donut-on-a-rope' trail, more clearly seen to the left of the picture....

Photo Copyright ©2000. Richard Cliff.  All Rights Reserved.

Just by seeing these two photographs you can see that by proof the aircraft that make these trails are just normal everyday jet aircraft.
I am by all means NOT saying that Steve did not see a black budget aircraft that day. However he may of just saw a very fast military jet....afterall he is near large Military Operating Areas.
With Steve being an Aviation Journalist i would expect him not to think all of a sudden that he saw a secret aircraft making that trail.
From the Distance of where he was to the relation of the vapour trail it is very unlikely he actually heard alot of noise..if any at all. The Jaguar above was at FL250 and it was not very loud at all....
The Jaguar has two reheated(afterburning) engines and makes alot of noise however when at altitude and depending on the throttle it can be quite silent. The same goes with any jet aircraft. whether it be secret or not.
Only Time will tell to see if the vapour trails some people see are actually fast moving secret aircraft with highly advanced engines.
I wrote this page to show people that normal aircraft can make any trail secret aircraft can....it just depends on the following:
Engine type
Movement
Speed
Altitude
Wind speed and direction at the aircrafts altitude.
and most important ;
Atmospheric Conditions of the surrounding and immediate area.