In principle, at least as clear as the Westclox-Mystery (you remember: The Westclox-Mystery) is the cooperation of the company Ingersoll with Junghans .
The brothers Charles and Robert Ingersoll founded in 1880 a mail order business in New York, 12 years later they sold first watches of the Waterbury Clock Company . Driven by the idea to automate the manufacture of movements in order to produce parts with the same quality, the brothers found models in the automotive industry, where a few years was produced on assembly lines. Ingersoll was one of the first companies that managed to make watch parts interchangeable thus enabling quick repairs and offer watches cheaply.
Legendary was the pocket model "Yankee" that was offered at a sensational sale price of $ 1 (then a daily wage equivalent) and was introduced in the year 1896.
Ingersoll started with the production of watches probably already from 1915 starting with the original lady's pocket Ingersoll "Midget" whose cases were provided with lugs, crown at three and draughty bracelets. Not infrequently, the watches were equipped with radium dials and contributed initially the addition "Radio Lite", later the model "nightlight" followed. These innovations catapulted Ingersoll in the first place of the watch producers. Apparently the Radio Lite watches were used by the tank crews of the English army in the WWI instead of previously used pocket watches. In the 20s of the last century Ingersoll promoted the production of wrist watches.
The year 1905 could have been groundbreaking for the cooperation with the company Junghans, because from this year Ingersoll traded with a branch in England (London) and from 1916 as an independent company, but only until 1922, when the company goes over to the Waterbury Clock Co. All of my watches, which include Junghans movements, date from 1931 - 1937, with the largest accumulation around the years 1931 - 1932.
This suggests that the cooperation could have been around the years 1931 - 1932 (meanwhile I have new clues that the collaboration took much longer, or was later resumed, more below ...).
Production data of the movements:
Ingersoll seems to have cooperated with various German watch companies, as well as with the company Thiel a cooperation is known around the turn of the century.
This shows also this watch, an Ingersoll Tudor (unfortunately without pointer) with a version of Thiel Divina (probably an early version around 1910):
But back to Ingersoll and Junghans. All but one (Spain) were purchased in England (including the Ingersoll Tudor/Thiel Divina).
All models are marked on the dial as well as on the movements with "FOREIGN".
The hands of the second watch, with the case missing, are original. Unfortunately, the hour hand is clearly bent at the base, in a possible bending attempt this would most likely break off.
A new door opens and brings a watch in the form of a new view to solve the Ingersoll puzzle - it looks as though the cooperation with Ingersoll went much longer than I suspected in the text above.
Due to the hitherto found watches my assumption was that the cooperation should have lain around the years 1931 - 1932. But that refutes the following watch that I found in England:
The watch is printed on the dial with INGERSOLL and SHOCK PROOF, above the small second located at 6 is LEVER 15 JEWEL, below the small second: FOREIGN
The back cover of the watch is without engraving, the movement (caliber Junghans J98/1 or Junghans 698.72) in turn shows both companies, the eight-pointed Junghans star with the J and the designation 98 for the caliber, below: Ingersoll 15 jewels lever
It is well known that the Junghans J98 was produced between 1951 and at least 1955. So the cooperation of the two companies in this time should be revived or entertained until then.
If somebody owns more watch receipts or information about the collaboration between Ingersoll and Junghans, I would be pleased about a short message!