I may have missed it, but what is the significance of the “AT” numbers? Obviously not all the ”AT” tools are for Packard Merlins, or even Whitworth.
I've looked at this before, Dave, and still have not found a definitive answer.
"AT" as an aircraft designation stands for Advanced Trainer.
"AT" as a parts designation does not appear in any period references I have, which includes a 1944 Navy Aviation Supply Office catalog and a 1943 H.M.S. Admiralty Fleet Order: Tool Kits for American Types of Aircraft. All my references, and especially the Navy ASO, are replete with stock number cross-references and indexes to help make supply easier. Tables and tables correlating parts. The Navy, including the Navy ASO, used the Federal Stock Number with an "R" prefix. Other common correlations include Naval Aircraft Factory numbers (NAF), Army Navy numbers (AN)(for parts interchangeable from Navy to Army Air Corps), US Army Air Corps numbers (AC), mfgrs codes (e.g., numbers unique to Wright, PWA, etc), and even some RAF numbers. I could flood the thread with excerpts, but suffice it to say, in every category you can think of, from nuts and bolts to hydraulic hose and couplings to extruded parts to hand tools to electronics, "AT" is very conspicuous
in its absence. Nuts and bolts and electronics are especially packed with parts listed by R, NAF, AN, AC, and in some cases RAF stock numbers. No "AT" anywhere to be found.
My theory is that it may indeed refer only to parts (including tools) associated with US equipment in British aircraft, such as Packard-built Merlin engines (Lancaster?), and whatever the Fairchild Ranger engines went in (Argus?). But my knowledge of US-British collaborations ends there.
Fairchild did make AT-21 Gunner trainers, which could complicate the problem.
Could we back ourselves into an answer empirically? Deriving it through the process of elimination?
Has anyone seen any WWII "AT" numbers on tools associated with aircraft
other than Packard Merlin and Fairchild Ranger or other US-British aviation hybrid kits? And were the Fairchild Ranger tools for British Lend-Lease aircraft or the AT-21 Gunner trainers?