Technical Question regarding WWII Bombers

In theory, the ZN is the squadron designator and the M is the aircraft designator within the squadron.  How ever this didn't always hold true.  Some RAF  wing Leaders or Group Captains were known for using their initials (IE Group Captain James E. ("Johnnie") used JE-J on his aircraft near the end of the war.)  And occasionally you will come across a pic  of two of the same type with the same designators (both squadron and in squadron designators) and one of them will have a dash painted under the in squadron designator indicating it is the second aircraft in the squadron with that letter in the squadron.  Hope this helps a little.

Sorry to muddy the waters but.  150 Squadron was coded DG or IQ.  ZN was on 106 Squadron.  But both squadrons flew Wellingtons during the war.

The info in the link below verifies SN #Z1608 was part of RAF 150 Sqdrn., but lists the codes as JN-M. Worth a look, if just for the information on this ship's last flight...

http://aircrewremembered.com/myall-ja.html

The RAF Web states that the JN code was used from September of 1939 to October 1944 to designate 150 squardon. In November '44, the code was changed to IQ.

http://www.rafweb.org/Sqn146-150.htm

Thanks all, this was a great help.  

Once you get the correct squadron codes and serial number sorted out, they are applied in pretty much a uniform fashion. The squadron and aircraft code letters flank the fuselage roundels- example: ZN@M, usually in large red letters on bombers. the aircraft serial numbers are applied in smaller red or black letters and numbers, depending upon the camouflage paint color there, on the fuselage sides near the vertical stabilizers.