USAAF & USAF Aircrew Log Book Mission Symbols
 

Can anyone advise on a source for decoding the Mission Symbols which were appended on USAAF and USAF aircrew Individual Flight Record forms?

These symbols usually comprise a letter followed by a number in the form “M-1”, “S-2”, “T-12” etc.

Ideally I’m interested in the WW2 to 1960 period. I’ve spoken to a number of crews from this period and all remember these symbols but can’t recall what each one meant!