Glossary of terms and abbreviations

Name: Dead letter drops
Explanation:

Used by civilian spies or couriers of the Special Duties Branch for leaving messages which were picked up and distributed by runners.

Name: Div
Explanation:

Division. Military unit, typically consisting of between 10,000 and 30,000 soldiers. 

Name: Div HQ
Explanation:

Divisional headquarters

Name: DoB
Explanation:

Defence of Britain Project. Volunteers of the DoB project recorded nearly 20,000 20th-century military sites.