During World War II the family was evacuated to Letchworth because of their dwelling's proximity to the London Docks, a major target of German bombing.
However, the pilpul (discourse) he delivered on the occasion of his barmitzva was heard by Rabbi Elya Lopian and Dayan Yehezkel Abramsky, two great Torah scholars who were living in Letchworth at the time.
He rapidly built up expertise in the areas of agunos and the correct spelling of names in gittin as well as in practical issues relating to mikvehs.
As his reputation grew Kaplin began to receive rabbinical questions from all over the world, and is quoted in such classic responsa as Minchas Yitschok and Yabia Omer.
[5] In retirement Kaplin moved to Jerusalem, Israel, where he was invited to serve as Rosh kollel of Rabbi Yitschok Myer Morgenstern's Yeshivas Toras Chochom.