Re: US Merchant Marines - Info on John Matthew Williams
The Merchant Marine was a civilan organization. Men who sailed on these ships belonged to a maritime union which posted openings on the boats that were setting out. A qualified hand was free to accept a position or stay ashore as it suited him.
The Merchant Marine was a relatively small organization that saw a significant proportion of it's members die during the war. They weren't sissies.
There are probably records from those days but, whether there is a file on every man is unknown to me.