Probably designed by Heighway in 1944 or early 1945, but not published until 1946 due to the lack of suitable card for manufacture. It may be that the previous publications, “B” through to “H”, were allowed supplies of scarce and rationed card, as they purported to be recognition models. J1 is obviously not a recognition model, so could not command the same resources from the Ministry of Supply during wartime. Its introduction had to await the post war easing of restrictions on paper.
The first advert announcing availability was in the Meccano magazine for August 1947.

The reader will have noted a jump in the sequence of numbering from H1 to J1. Researchers do not consider that there ever was a kit numbered “I1”. It is normal drawing office practice to leave out the letter “I” so as to prevent any misinterpretation with the number “1”.
Unfortunately, the single sheet road vehicle Tank Lorry AEC Monarch issued by Modelcraft in 1947 also has the “Series J. Set No. 1” number.

Large quantities of J1 Stephenson’s Rocket seem to have passed to the ERG Model shop in 1979.

The Micromodels Ltd. set H1 Famous Historic Locos has some obvious similarities with set J1.

Myles Mandell issued Stephenson’s Rocket in the early 1980s. The model is basically the set J1, but scaled up approximately 2x. The model was completely redrawn and features were added such as detailed instructions and planagraphs.