bn orders for 2RSF - what is an MDB?

Hi All,
just going through some old bn orders for 2RSF and I have come across a statement I'd like translating please!
Posted to "Y" list 11.12.40
Re posted to Bn 19.12.40 on release from M.D.B. Chorley.

any thoughts?
thanks in advance.

 

one more.... how does someone qualify for "War time proficiency pay"?

 

MDB Military Detention Barracks

 

aha! thanks Snailer.

 

I was going to suggest Movie Database before the internet was invented.