Could this be your man Berry?
https://discovery.nationalarchives.gov.uk/details/r/C8331995If so this would be his seamans "Pouch"
Records relating to individual seamen filed together in a pouch. These documents may include application forms (most with a photograph of the seaman), certificates, identity cards, cessation documents and notifications of death.
What you really need is his Form CRS10. This will give details of all the ships he served on, with dates and places of Engagement and Discharge. If it has survived it will be in the series BT382.For security reasons, You would need to visit Kew or appoint an independent researcher to look for you.
If you are prepared to do that I will post details later.
Have a day out at Kew and pick up his "Pouch" at the same time.
PS Can you give us the name of your home town in Germany?