Operational Base Design

See also: Base Overview - Tour an Operational Base - OB Discipline - View database of bases around the UK

This page was last updated at 2:00 pm on 29/11/11

The primary requirements for OBs were that they should be concealed, habitable and reasonably weatherproof.  A standard design was used, comprising an underground chamber with a vertical shaft at one end leading to the main entrance, and an escape passage at the other end.  The entrances were secured with well camouflaged trapdoors.  Because of the camouflage and secrecy associated with these structures, they are generally poorly represented in records of known sites from the period.

(Above - The training OB at Coleshill we believe served as a prototype.  Take a tour of this OB here.)

Designs varied from County to County.

Suffolk and Norfolk: The first OBs to be constructed were built in East Anglia (in Essex and South Suffolk), often by the patrol members themselves and later with the help of Royal Engineers. Norfolk and Suffolk OBs typically consisted of a main chamber, a so-called 'Elephant' shelter, which had a curved, corrugated iron roof (similar to a Nissen hut but underground). Main chambers varied in length from 12-15ft. The end walls could be brick, or earth lined/stabilised with corrugated sheeting. The main chamber was accessed through a drop-down shaft, either built from brick, or they had earthen walls that were lined with corrugated sheeting. Most but not all had an underground escape passage of several metres' length that led out the other end. Both entrance and exit openings were secured with well disguised trapdoors commonly operated with counterweights.

An example can be seen here  

Lincolnshire: Typical Lincolnshire OBs are sturdily built structures made from concrete prefabricated panels that were bolted together (rather like a Stanton shelter but underground), and brick or breezeblock end walls. The main chamber was accessed through a drop-down, breezeblock-built shaft. Main chambers varied in length from 12-14ft and appear to have been well ventilated. The walls of emergency exit tunnels were commonly also built from breezeblocks, and a toilet cubicle and even an ammunition store can often be found incorporated in the structure. Both entrance and exit openings were secured with well disguised trapdoors or hatches. The use of counterweights appears to have been less common in Lincolnshire than it was in both Suffolk and Norfolk.

An example can be seen here

Dorset: Most OBs seem to be built with the standard Elephant shelter, though 2 chambers seem common. End walls are brick and escape tunnels, where present, were presumably wood or corrugated iron as most seem to have collapsed. It is known that the Pioneer Corps built at least one OB. No surviving lids have been found yet, but there is evidence of recessed hatches in a couple of surviving shafts. Some OBs seem to have been built relatively late on (late 1942).

Scotland: Operational Bases were a ‘variation on a theme’ as compared to some of the Scottish Mainland ones. Improvisation being the operative word and islanders from these parts were a hardy lot. It was A.G Fiddes-Watt Intelligence Officer (IO) for Number 1 Area; who looked on in sheer horror as ancient pot sherds were discarded by some members of a patrol while they were hastily constructing their OB.

Other counties will follow.

These OB plans were sent to us by Jeff Bubble. You can download the full unedited large version here

Sgt Fred Trego's Trap Door Plans. Read more about Fred's Patrol here.
These images are © DSBrown/NTrego

A top secret file, found at The Aux Museum at Parham, gives detailed information about the camouflaging of OB doors. It can now be downloaded here.

If you would like to go into an Operational Base but not get covered in dirt and grime why not try the mock up OB at The Auxiliary Museum, Parham Suffolk?