My dad Stanley G Henry was on a ship in World War 2.
From what I remember he was a cook on there. He was born 25 Nov 1915 and lied about his age so he could go fight.
How can I find his number or the name of the ship he was on?
If your Dad was in the Royal Navy, rather than the merchant navy:
WW2 service records are still held by the Ministry of Defence; this page on the MOD website tells you how you can get a copy: https://www.gov.uk/get-copy-military-service-records/apply-for-someone-elses-records.
Merchant Navy
Merchant Navy records up to 1941 are held by The National Archives (TNA) and have been digitised by Find My Past; you can read more about them here: https://www.nationalarchives.gov.uk/help-with-your-research/research-guides/merchant-seamen-registers-1918-1941/
You might also find him in the campaign medal files: https://www.nationalarchives.gov.uk/help-with-your-research/research-guides/merchant-seamens-campaign-medal-records-1939-1945/
There may be other records available, see these other guides from TNA. https://www.nationalarchives.gov.uk/help-with-your-research/research-guides-keywords/?show=keywords&keyword-letter=m&keyword=merchant-navy-1#step-three
I have no naval research experience myself so I have no idea how difficult it might be to find the information you seek; there may well be other sources you can check, too.
Being new myself, I can only answer, not comment.
I noticed there is no mention of whether or not the ship your dad served on was sunk or not. I did a fair bit of research myself on two distant relations (one merchant marine and one fisherman - both of Scotland).
I unknowingly stumbled into an awesome site for the Tower Hill Memorial in the UK: https://www.benjidog.co.uk/Tower%20Hill/ If Brian can't steer you in the right direction I will be surprised.
I found too that another great way to find ship information and images was to Google 'the vessel -----' and select the images option. (replace --- with any vessel name). It led me to many great information sites; one being: https://www.wrecksite.eu/Wrecksite.aspx
Many of these sites you can search by a persons name. If you are a member of any of the ancestry sites that provide 'hints and tips' just entering your father's name and info with his parents, spouse, or other family member usually generates clues as to military service.
I just found this and will add it here: https://en.wikipedia.org/wiki/Category:Royal_Navy_personnel_of_World_War_II
I've only recently cleared the brick wall that was behind my own father. It's been an interesting journey.
CHECK YOUR ANCESTRY MESSAGES
Best of luck :)