ALLEYN’S SCHOOL J.T.C white embroidery on black wool backing cloth shoulder title.

Rare mint condition ALLEYN’S SCHOOL J.T.C white embroidery on black wool backing cloth shoulder title.

The JTC system generally

Alleyn’s cadet unit began life as part of the Officers’ Training Corps, formed in 1908 under the Haldane reforms, with a “Junior Division” specifically for public schools. Towards the end of 1940 (some sources say early 1941), the War Office renamed all these school units from OTC to Junior Training Corps (JTC), reportedly to shed the “elitist” OTC name at a moment when wartime social cohesion mattered. The JTC designation lasted until 1948, when the JTCs were folded into the newly formed Combined Cadet Force, so your dating (1940–1948) matches the accepted timeline exactly.

Alleyn’s School itself

Alleyn’s is the Dulwich day school founded in 1619, part of Edward Alleyn’s original College of God’s Gift foundation alongside Dulwich College and James Allen’s Girls’ School. It became a distinct boys’ school in 1882. I couldn’t find a dedicated published history of Alleyn’s own JTC unit specifically (no unit numbers, commanding officers, or founding date for their JTC turned up in searchable sources), only the general national chronology above, which the badge itself confirms by using “J.T.C.” rather than “O.T.C.” or “C.C.F.”