Index and link to images for Bremen Civil registration records are available at this link: https://die-maus-bremen.info/index.php?id=29
Archive website with images: https://www.arcinsys.niedersachsen.de/arcinsys/detailAction.action?detailid=v8580632
Source of information: Archion forum: https://www.archion.de/en/forum/threads/meilenstein-f%C3%BCr-die-genealogie-%E2%80%93-bremische-personenstandsregister-zivilstandsregister-und-stammtafeln-online.16255/
Military records are available on Ancestry.com. These include Restanten lists which sometimes list emigrants who went to America without military permission. See this collection: https://www.ancestry.com/search/collections/60899/
Bremen Bürgerbücher: https://die-maus-bremen.info/fileadmin/pdf_docs/blaetter_der_1-12/Band%2001%20Ergaenzung%201925.pdf
Ortssippenbuch Bremerhaven: https://ofb.genealogy.net/bremerhaven/?lang=de