The first stamps produced especially for the German colony in Karolinen were overprinted versions of German Krone / Adler issues.
This series was first available for use on 12 October 1899.
In May 1900, a second set of overprints was introduced bearing the same “Karolinen” overprint, but at a steeper angle (56°). The 48° Overprints are much rarer, and are valued as such.
The 3 Pf and 25 Pf can be found with plate flaws on the underlying stamps.