Curious to know if there was a 'rhyme or reason' as to which clocks went into specific WWII aircraft. The size of the clock obviously dictated which clock would go, but why were there larger clocks made for aircraft?

Here are two examples- The clock face of the left came from a C-45 trainer crash from 1942. It is larger and must more elegant-looking with the main clock, an 8 Day, and Elapsed Time. No idea who made this clock.

The Elgin clock on the right came from a B-17 crash from 1943(training flight with engine trouble forced the pilot to set the bomber down on the desert- the crew was able to escape, but the plane was consumed by flames.) This is the standard size aircraft clock.

Certainly the C-45 had a amount for the standard size clock, but somehow ended up with the larger one. It would seem that the larger aircraft would be allotted the larger, elaborate clocks.

Was it just the luck of the draw?

Obviously the one on the left, the larger one, is a multi-function clock, and thus the larger size, while the other is just a time-teller.

The amount of room in a cockpit was not so tight that it would make much difference between installing a 2 inch and 3 inch clock. There were a number of 3 inch and 2 instruments of various types in every aircraft. The reason some aircraft had the more complicated clocks was due to whether they really needed them. For example, the long range reconnaisance aircraft like the PBY had large complicated clocks because they really needed them on those very long flights.

And many of the larger aircraft often had more than one clock in them. For example, not only the pilot needed one, but often the radio operator/navigator also needed one at their station. And if the crew included a flight engineer sometimes his station had one with his instruments that he used to monitor the engines.

The generic, one size fits most clock was the A-11 which is the one on the right that came from the B-17.

Unless you recover a relic from an actual crash, or unless you have rock hard provenance from someone who removed the clock of an actual aircraft (vet's memories and stories about where clocks in their possession came from seem to be about 90 percent incorrect - either partially or totally), there is really no way to tell exactly what kind of an aircraft a particular clock was in. And that is further complicated by the fact that these clocks (and all aircraft instruments0 were regularly removed from aircraft for servicing and often they were reinstalled in different aircraft afterwards since they were so interchangeable.

Thanks for the clarification. There were many 2 and 3 inch holes in the instrument dash so I was curious if there was a strict rule as to which aircraft were given different size/ style clocks. It sounds like the standard 2-inch A-11 clock was found in most WWII aircraft (single or multi-engine), but the elaborate 3-inch would be predominately found on multi-engine aircraft that relied heavily on complex navigation, long-range patrol, or training.

Finding these old WWII crash sites has been a 20 year 'hobby' of mine and everything is properly photographed and documented with the crash date, a/c type & serial number, location, crew names, etc... I have come across many of the A-11 clock faces but the 3-inch face on the left is the only one I have seen, hence the curiosity.

Your 3 inch dial came from a Jaeger LeCoultre A-10 Chronoflite Elapsed Time Clock. These were made during the pre-war and early war era. Later in the war production switched to the more complicated Hamilton-Elgin 37500 Elapsed Time clock which had the main dial plus 4 subsidiary dials. There was another 3 inch dial clock with production that overlapped these two more complicated clocks during the war that was the Waltham CDIA which stands for Civilian Date Indicator Aeronautical clock. This has the main dial along with a second small dial centered on the main dial with a hand that pointed at the date (from 1 to 31). There were also a few pre-war 3 inch dial clocks with no extra dials that were still around during the war.

The basic 2 inch dial A-11s were the real workhorses during the war, though.