I found the answer to the question I asked above:
Watchtower Baptismal Requirements
Prior to 1951 - Baptism as a Christian in any religion, provided by full water immersion. (What Pastor Russell Said pp.35,36)
1955 to 1985 - Baptised by Watchtower Representative to Father, Son and Holy Spirit.
1985 onwards - Baptised by Watchtower Representative to Father, Son and the Organization (w85 6/1 p.30)
Baptismal questions from the Watchtower 1956 Jul 1 p.407:
(1) Have you recognized yourself before Jehovah God as a sinner who needs salvation, and have you acknowledged to him that this salvation proceeds from him the Father through his Son Jesus Christ?
(2) On the basis of this faith in God and in his provision for salvation, have you dedicated yourself unreservedly to God to do his will henceforth as he reveals it to you through Jesus Christ and through the Bible under the enlightenment of the holy spirit?"
This was in effect until it was changed in the Watchtower 1966 Aug 1 p.465.