Complex sentence: As staff moved into their new offices foundations were being laid for a factory block to the east of the original building; this new block came to be known as Building No.3 and was complete and fully operational by February 1933.
Split into simpler sentences: As staff moved into there new offices foundations were being laid for a factory block to the east of the original building. The factory block which came to be known as building No.3 was complete and fully operational by February 1933.