Complex sentence: The bulk of the ratings were enlisted as "Hostilities Only" and all had to be trained in which ever branch of the Navy they had chosen to serve, after about six weeks drilling, marching and generally getting physically fit they moved onto specific job training.
Split into simpler sentences: The bulk of the ratings were enlisted as "Hostilities Only" and all had to be trained in which ever branch of the Navy they had chosen to serve. After about six weeks drilling, marching and generally getting physically fit they moved onto specific job training.