It is known that Timex was working on a Mil-Spec back in the mid to early 60's. Although they never went full production there were several models that came out for civilian use. The first was the 1966 24 hr black dial Sprite. That was the model at J Crew turned into a reissue. Other models were the Funtimer's from 1967 which used the plastic case. The final model was the Camper which is model copied for the MK1. Here is the Sprite
rare is a difficult word to apply but, since the 400 series was only produced for two years there are certainly less of them. The 21 ran for well over 12 years or more so lots them out there.
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