In Search of Christian Freedom, by Ray Franz, page 489, footnote number 1:
Scholars recognize that "Jehovah" is not an accurate rendering of the Tetragrammaton; many believe "Yahweh" comes closest to the correct pronunciation of the Hebrew. In its original "Foreword", the Watch Tower's New World Translation stated: "While inclining to view the pronunciation Yah.weh as the more correct way, we have retained the form Jehovah because of people's familiarity with it since the 14th century". See New World Translation of the Christian Greek Scriptures, page 25.
Now, let's give the floor to the Jewish Encyclopaedia (http://www.jewishencyclopedia.com/view.jsp?artid=206&letter=J&search=jehovah
A mispronunciation (introduced by Christian theologians, but almost entirely disregarded by the Jews) of the Hebrew "Yhwh," the (ineffable) name of God (the Tetragrammaton or "Shem ha-Meforash"). This pronunciation is grammatically impossible; it arose through pronouncing the vowels of the "?ere" (marginal reading of the Masorites:
The reading "Jehovah" is a comparatively recent invention. The earlier Christian commentators report that the Tetragrammaton was written but not pronounced by the Jews (see Theodoret, "Question. xv. in Ex." [Field, "Hexapla," i. 90, to Ex. vi. 3]; Jerome, "Præfatio Regnorum," and his letter to Marcellus, "Epistola," 136, where he notices that "PIPI" [= ΠIΠI = see also Aquila).
"Jehovah" is generally held to have been the invention of Pope Leo X.'s confessor, Peter Galatin ("De Arcanis Catholicæ Veritatis," 1518, folio xliii.), who was followed in the use of this hybrid form by Fagius (= Büchlein, 1504-49). Drusius (= Van der Driesche, 1550-1616) was the first to ascribe to Peter Galatin the use of "Jehovah," and this view has been taken since his days (comp. Hastings, "Dict. Bible," ii. 199, s.v. "God"; Gesenius-Buhl, "Handwörterb." 1899, p. 311; see Drusius on the tetragrammaton in his "Critici Sacri, i. 2, col. 344). But it seems that even before Galatin the name "Jehovah" had been in common use (see Drusius, l.c. notes to col. 351). It is found in Raymond Martin's "Pugio Fidei." written in 1270 (Paris, 1651, iii., pt. ii., ch. 3, p. 448; comp. T. Prat in "Dictionnaire de la Bible," s.v.). See also Names of God.
The pronunciation "Jehovah" has been defended by Stier ("Hebr. Lehrgebäude") and Hölemann ("Bibelstudien.," i.).
The use of the composite "shewa" "?atef segol" (i.e.,
Read more: http://www.jewishencyclopedia.com/view.jsp?artid=206&letter=J&search=jehovah#ixzz0jQuVScCl
Catholics also recognize "Jehovah" as "the name of God in the Old Testament". Which is to say they make the same mistake.
http://www.newadvent.org/cathen/08329a.htm