[maryz]

When a Protestant converts to Catholicism the Catholic Church does not baptize them again because they have already been baptized in another Christian church. Catholics recognize Protestants as Christian.

When I was in a Catholic high school in the 60s, we learned that in the case of a Protestant converting to Catholicism, he received "conditional Baptism" -- i.e., "If thou art not already baptized, I baptize thee ..."

[paterfamilias]

“When I was in a Catholic high school in the 60s, we learned that in the case of a Protestant converting to Catholicism, he received “conditional Baptism” — i.e., ‘If thou art not already baptized, I baptize thee ...’”

This seems quite plausible.