The "D" frame Colt's had the shrouded barrel/ramped front sight, starting with the Detective Special in 1972. The Agent and Cobra followed immediately.
Which issue that would be depends on who you talk to. I would say it's the 3rd issue.
The first issue ran from 1927 to the end of WWII.
The second issue ran from WWII to 1972 and was a change to a shorter grip frame, with grips that wrapped under the stubby grip frame.
The 3rd issue was introduced in 1972, and had the shouded barrel, and the oversized "combat" grips.
The "4th issue" is the same as the 3rd, being nothing but a short run made in the mid to late 90's, after Colt discontinued the "D" frames in the late 80's. The only real difference, is the 4th issue have the rubber Pacmayer grips, and the blue plastic box. Many of these were made up from left over parts.
So, the shrouded guns were made from 1972 to around the late 80's. There was then a period where the various "D" frame guns were discontinued, re-introduced, and discontinued again in a bewildering sequence.
The "D" guns were finally discontinued permanently??? in favor of the SF-VI/DS-II gun, which was itself discontinued.
[This message has been edited by dfariswheel (edited 02-05-2002).]