Marvin E. Whitney, Military Timepieces, 1992, pp. 153-158
After the attack on Pearl Harbor the U.S. government instructed Hamilton and the Elgin National Watch Co. to make a 30-hour and an 8-day marine chronometer. Hamilton had a far better set-up for increasing production whilst Elgin had to start from scratch having never made marine chronometers before. Their first chronometer was accepted by the Naval Observatory after considerable adjustments but the next 22 all failed. Shortly afterwards the war ended and the contract was cancelled. Approximately 250 only of Elgin's Model 600 were sold to the public and today they are possibly the rarest 'mass-produced' chronometers on the clock market.