There were three 1911-style Colt .22's - none of them a conversion as we know it, but made as .22's.
One was meant to be as close to GI as possible, including recoil - the original Service Ace, with the floating chamber & parkerized or blue finish, made 1935-45 ("SM" prefix serial to about 13,900).
Some of these may have been (GI) issued, as specimens have been seen with "USCG" & "U.S,PROP'Y" marks and/or a gov't inspector's mark, like "RS".
There was also the commercial Ace, (ser #1 - 10,935) made 1931-41 & in 1947; and the post-war Service Ace, made by the Colt Custom Shop 1978-82 in blue or electroless nickle (Serial # has either "SM" prefix or B70 suffix).
There was a non-firearm .45ACP-to-.22LR conversion unit made/sold commercially, consisting of slide/barrel/spring/guide/magazine, from 1938-1954, some of which have been documented as issued to USMC - copied by other companies today, such as Ceiner, Kimber, etc.
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